diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Auth.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Auth.cs
new file mode 100644
index 00000000..f08b6c95
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Auth.cs
@@ -0,0 +1,14 @@
+namespace EnvelopeGenerator.API.Models;
+
+public record Auth(string? AccessCode = null, string? SmsCode = null, string? AuthenticatorCode = null, bool UserSelectSMS = default)
+{
+    public bool HasAccessCode => AccessCode is not null;
+
+    public bool HasSmsCode => SmsCode is not null;
+
+    public bool HasAuthenticatorCode => AuthenticatorCode is not null;
+
+    public bool HasMulti => new[] { HasAccessCode, HasSmsCode, HasAuthenticatorCode }.Count(state => state) > 1;
+
+    public bool HasNone => !(HasAccessCode || HasSmsCode || HasAuthenticatorCode);
+}
\ No newline at end of file
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/ContactLink.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/ContactLink.cs
new file mode 100644
index 00000000..691dbc83
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/ContactLink.cs
@@ -0,0 +1,60 @@
+namespace EnvelopeGenerator.API.Models
+{
+    /// <summary>
+    /// Represents a hyperlink for contact purposes with various HTML attributes.
+    /// </summary>
+    public class ContactLink
+    {
+        /// <summary>
+        /// Gets or sets the label of the hyperlink.
+        /// </summary>
+        public string Label { get; init; } = "Contact";
+
+        /// <summary>
+        /// Gets or sets the URL that the hyperlink points to.
+        /// </summary>
+        public string Href { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Gets or sets the target where the hyperlink should open.
+        /// Commonly used values are "_blank", "_self", "_parent", "_top".
+        /// </summary>
+        public string Target { get; set; } = "_blank";
+
+        /// <summary>
+        /// Gets or sets the relationship of the linked URL as space-separated link types.
+        /// Examples include "nofollow", "noopener", "noreferrer".
+        /// </summary>
+        public string Rel { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Gets or sets the filename that should be downloaded when clicking the hyperlink.
+        /// This attribute will only have an effect if the href attribute is set.
+        /// </summary>
+        public string Download { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Gets or sets the language of the linked resource. Useful when linking to
+        /// content in another language.
+        /// </summary>
+        public string HrefLang { get; set; } = "en";
+
+        /// <summary>
+        /// Gets or sets the MIME type of the linked URL. Helps browsers to handle
+        /// the type correctly when the link is clicked.
+        /// </summary>
+        public string Type { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Gets or sets additional information about the hyperlink, typically viewed
+        /// as a tooltip when the mouse hovers over the link.
+        /// </summary>
+        public string Title { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Gets or sets an identifier for the hyperlink, unique within the HTML document.
+        /// </summary>
+        public string Id { get; set; } = string.Empty;
+    }
+
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Culture.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Culture.cs
new file mode 100644
index 00000000..b1386088
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Culture.cs
@@ -0,0 +1,17 @@
+using System.Globalization;
+
+namespace EnvelopeGenerator.API.Models;
+
+public class Culture
+{
+    private string _language = string.Empty;
+    public string Language { get => _language;
+        init {
+            _language = value;
+            Info = new(value);
+        } 
+    }
+    public string FIClass { get; init; } = string.Empty;
+
+    public CultureInfo? Info { get; init; }
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Cultures.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Cultures.cs
new file mode 100644
index 00000000..7b293c13
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Cultures.cs
@@ -0,0 +1,12 @@
+namespace EnvelopeGenerator.API.Models;
+
+public class Cultures : List<Culture>
+{
+    public IEnumerable<string> Languages => this.Select(c => c.Language);
+
+    public IEnumerable<string> FIClasses => this.Select(c => c.FIClass);
+
+    public Culture Default => this.First();
+    
+    public Culture? this[string? language] => language is null ? null : this.Where(c => c.Language == language).FirstOrDefault();
+}
\ No newline at end of file
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/CustomImages.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/CustomImages.cs
new file mode 100644
index 00000000..fd212acd
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/CustomImages.cs
@@ -0,0 +1,6 @@
+namespace EnvelopeGenerator.API.Models;
+
+public class CustomImages : Dictionary<string, Image>
+{
+    public new Image this[string key] => TryGetValue(key, out var img) && img is not null ? img : new();
+}
\ No newline at end of file
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/EnvelopeReceiverLogin.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/EnvelopeReceiverLogin.cs
new file mode 100644
index 00000000..fa53ec61
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/EnvelopeReceiverLogin.cs
@@ -0,0 +1,7 @@
+namespace EnvelopeGenerator.API.Models;
+
+/// <summary>
+/// Request body for the envelope-receiver login endpoint.
+/// </summary>
+/// <param name="AccessCode">The access code sent to the receiver.</param>
+public record EnvelopeReceiverLogin(string? AccessCode = null);
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/ErrorViewModel.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/ErrorViewModel.cs
new file mode 100644
index 00000000..b09ffded
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/ErrorViewModel.cs
@@ -0,0 +1,10 @@
+namespace EnvelopeGenerator.API.Models;
+
+public class ErrorViewModel
+{
+    public string Title { get; init; } = "404";
+
+    public string Subtitle { get; init; } = "Hmmm...";
+
+    public string Body { get; init; } = "It looks like one of the developers fell asleep";
+}
\ No newline at end of file
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Image.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Image.cs
new file mode 100644
index 00000000..d7abd148
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Image.cs
@@ -0,0 +1,10 @@
+namespace EnvelopeGenerator.API.Models;
+
+public class Image
+{
+    public string Src { get; init; } = string.Empty;
+
+    public Dictionary<string, string> Classes { get; init; } = new();
+
+    public string GetClassIn(string page) => Classes.TryGetValue(page, out var cls) && cls is not null ? cls : string.Empty;
+}
\ No newline at end of file
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Login.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Login.cs
new file mode 100644
index 00000000..926b1811
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/Login.cs
@@ -0,0 +1,13 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace EnvelopeGenerator.API.Models;
+
+/// <summary>
+/// Repräsentiert ein Login-Modell mit erforderlichem Passwort und optionaler ID und Benutzername.
+/// </summary>
+/// <param name="Password">Das erforderliche Passwort für das Login.</param>
+/// <param name="UserId">Die optionale ID des Benutzers.</param>
+/// <param name="Username">Der optionale Benutzername.</param>
+public record Login([Required] string Password, int? UserId = null, string? Username = null)
+{
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/MainViewModel.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/MainViewModel.cs
new file mode 100644
index 00000000..d49d323b
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/MainViewModel.cs
@@ -0,0 +1,6 @@
+namespace EnvelopeGenerator.API.Models;
+
+public class MainViewModel
+{
+    public string? Title { get; init; }
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Annotation.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Annotation.cs
new file mode 100644
index 00000000..5dbb1aed
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Annotation.cs
@@ -0,0 +1,93 @@
+using EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+using System.Text.Json.Serialization;
+
+namespace EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+
+public record Annotation : IAnnotation
+{
+    public required string Name { get; init; }
+
+    #region Bound Annotation
+    [JsonIgnore]
+    public string? HorBoundAnnotName { get; init; }
+
+    [JsonIgnore]
+    public string? VerBoundAnnotName { get; init; }
+    #endregion
+
+    #region Layout
+    [JsonIgnore]
+    public double? MarginLeft { get; set; }
+
+    [JsonIgnore]
+    public double MarginLeftRatio { get; init; } = 1;
+
+    [JsonIgnore]
+    public double? MarginTop { get; set; }
+
+    [JsonIgnore]
+    public double MarginTopRatio { get; init; } = 1;
+
+    public double? Width { get; set; }
+
+    [JsonIgnore]
+    public double WidthRatio { get; init; } = 1;
+
+    public double? Height { get; set; }
+
+    [JsonIgnore]
+    public double HeightRatio { get; init; } = 1;
+    #endregion
+
+    #region Position
+    public double Left => (MarginLeft ?? 0) + (HorBoundAnnot?.HorBoundary ?? 0);
+
+    public double Top => (MarginTop ?? 0) + (VerBoundAnnot?.VerBoundary ?? 0);
+    #endregion
+
+    #region Boundary
+    [JsonIgnore]
+    public double HorBoundary => Left + (Width ?? 0);
+
+    [JsonIgnore]
+    public double VerBoundary => Top + (Height ?? 0);
+    #endregion
+
+    #region BoundAnnot
+    [JsonIgnore]
+    public Annotation? HorBoundAnnot { get; set; }
+
+    [JsonIgnore]
+    public Annotation? VerBoundAnnot { get; set; }
+    #endregion
+
+    public Color? BackgroundColor { get; init; }
+
+    #region Border
+    public Color? BorderColor { get; init; }
+
+    public string? BorderStyle { get; init; }
+
+    public int? BorderWidth { get; set; }
+    #endregion
+
+    [JsonIgnore]
+    internal Annotation Default 
+    { 
+        set 
+        {
+            // To set null value, annotation must have null (0) value but null must has non-null value
+            if (MarginLeft == null && value.MarginLeft != null)
+                MarginLeft = value.MarginLeft * MarginLeftRatio;
+
+            if (MarginTop == null && value.MarginTop != null)
+                MarginTop = value.MarginTop * MarginTopRatio;
+
+            if (Width == null && value.Width != null)
+                Width = value.Width * WidthRatio;
+
+            if (Height == null && value.Height != null)
+                Height = value.Height * HeightRatio;
+        }
+    }
+};
\ No newline at end of file
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/AnnotationParams.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/AnnotationParams.cs
new file mode 100644
index 00000000..019d872e
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/AnnotationParams.cs
@@ -0,0 +1,80 @@
+using EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+using System.Text.Json.Serialization;
+
+namespace EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+
+public class AnnotationParams
+{
+    public AnnotationParams()
+    {
+        _AnnotationJSObjectInitor = new(CreateAnnotationJSObject);
+    }
+
+    public Background? Background { get; init; }
+
+    #region Annotation
+    [JsonIgnore]
+    public Annotation? DefaultAnnotation { get; init; }
+
+    private readonly List<Annotation> _annots = new List<Annotation>();
+
+    public bool TryGet(string name, out Annotation annotation)
+    {
+#pragma warning disable CS8601 // Possible null reference assignment.
+        annotation = _annots.FirstOrDefault(a => a.Name == name);
+#pragma warning restore CS8601 // Possible null reference assignment.
+        return annotation is not null;
+    }
+
+    public required IEnumerable<Annotation> Annotations
+    {
+        get => _annots;
+        init
+        {
+            _annots = value.ToList();
+
+            if (DefaultAnnotation is not null)
+                foreach (var annot in _annots)
+                    annot.Default = DefaultAnnotation;
+
+            for (int i = 0; i < _annots.Count; i++)
+            {
+                #region set bound annotations
+                // horizontal
+                if (_annots[i].HorBoundAnnotName is string horBoundAnnotName)
+                    if (TryGet(horBoundAnnotName, out var horBoundAnnot))
+                        _annots[i].HorBoundAnnot = horBoundAnnot;
+                    else
+                        throw new InvalidOperationException($"{horBoundAnnotName} added as bound anotation. However, it is not defined.");
+
+                // vertical
+                if (_annots[i].VerBoundAnnotName is string verBoundAnnotName)
+                    if (TryGet(verBoundAnnotName, out var verBoundAnnot))
+                        _annots[i].VerBoundAnnot = verBoundAnnot;
+                    else
+                        throw new InvalidOperationException($"{verBoundAnnotName} added as bound anotation. However, it is not defined.");
+                #endregion
+            }
+        }
+    }
+    #endregion
+
+    #region AnnotationJSObject
+    private Dictionary<string, IAnnotation> CreateAnnotationJSObject()
+    {
+        var dict = _annots.ToDictionary(a => a.Name.ToLower(), a => a as IAnnotation);
+
+        if (Background is not null)
+        {
+            Background.Locate(_annots);
+            dict.Add(Background.Name.ToLower(), Background);
+        }            
+
+        return dict;
+    }
+
+    private readonly Lazy<Dictionary<string, IAnnotation>> _AnnotationJSObjectInitor;
+
+    public Dictionary<string, IAnnotation> AnnotationJSObject => _AnnotationJSObjectInitor.Value;
+    #endregion
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Background.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Background.cs
new file mode 100644
index 00000000..19298196
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Background.cs
@@ -0,0 +1,58 @@
+using System.Text.Json.Serialization;
+
+namespace EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+
+/// <summary>
+/// The Background is an annotation for the PSPDF Kit. However, it has no function.
+/// It is only the first annotation as a background for other annotations.
+/// </summary>
+public record Background : IAnnotation
+{
+    [JsonIgnore]
+    public double Margin { get; init; }
+
+    public string Name { get; } = "Background";
+
+    public double? Width { get; set; }
+
+    public double? Height { get; set; }
+
+    public double Left { get; set; }
+
+    public double Top { get; set; }
+
+    public Color? BackgroundColor { get; init; }
+
+    #region Border
+    public Color? BorderColor { get; init; }
+
+    public string? BorderStyle { get; init; }
+
+    public int? BorderWidth { get; set; }
+    #endregion
+
+    public void Locate(IEnumerable<IAnnotation> annotations)
+    {
+        // set Top
+        if (annotations.MinBy(a => a.Top)?.Top is double minTop)
+            Top = minTop;
+
+        // set Left
+        if (annotations.MinBy(a => a.Left)?.Left is double minLeft)
+            Left = minLeft;
+
+        // set Width
+        if(annotations.MaxBy(a => a.GetRight())?.GetRight() is double maxRight)
+            Width = maxRight - Left;
+
+        // set Height
+        if (annotations.MaxBy(a => a.GetBottom())?.GetBottom() is double maxBottom)
+            Height = maxBottom - Top;
+
+        // add margins
+        Top -= Margin;
+        Left -= Margin;
+        Width += Margin * 2;
+        Height += Margin * 2;
+    }
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Color.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Color.cs
new file mode 100644
index 00000000..0d3d4056
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Color.cs
@@ -0,0 +1,10 @@
+namespace EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+
+public record Color
+{
+    public int R { get; init; } = 0;
+
+    public int G { get; init; } = 0;
+
+    public int B { get; init; } = 0;
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Extensions.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Extensions.cs
new file mode 100644
index 00000000..1cc508fd
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/Extensions.cs
@@ -0,0 +1,8 @@
+namespace EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+
+public static class Extensions
+{
+    public static double GetRight(this IAnnotation annotation) => annotation.Left + annotation?.Width ?? 0;
+
+    public static double GetBottom(this IAnnotation annotation) => annotation.Top + annotation?.Height ?? 0;
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/IAnnotation.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/IAnnotation.cs
new file mode 100644
index 00000000..735bf573
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/PsPdfKitAnnotation/IAnnotation.cs
@@ -0,0 +1,22 @@
+namespace EnvelopeGenerator.API.Models.PsPdfKitAnnotation;
+
+public interface IAnnotation
+{
+    string Name { get; }
+
+    double? Width { get; }
+
+    double? Height { get; }
+
+    double Left { get; }
+
+    double Top { get; }
+
+    Color? BackgroundColor { get; }
+
+    Color? BorderColor { get; }
+
+    string? BorderStyle { get; }
+
+    int? BorderWidth { get; }
+}
diff --git a/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/TFARegParams.cs b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/TFARegParams.cs
new file mode 100644
index 00000000..ff363fdf
--- /dev/null
+++ b/EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI/Models/TFARegParams.cs
@@ -0,0 +1,17 @@
+namespace EnvelopeGenerator.API.Models;
+
+/// <summary>
+/// Represents the parameters for two-factor authentication (2FA) registration.
+/// </summary>
+public class TFARegParams
+{
+    /// <summary>
+    /// The maximum allowed time for completing the registration process.
+    /// </summary>
+    public TimeSpan TimeLimit { get; init; } = new(0, 30, 0);
+
+    /// <summary>
+    /// The deadline for registration, calculated as the current time plus the <see cref="TimeLimit"/>.
+    /// </summary>
+    public DateTime Deadline => DateTime.Now.AddTicks(TimeLimit.Ticks);
+}
\ No newline at end of file