Add project files.

DXApp.TemplateKitProject/Pages/About.cshtml

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+@page
+<h2 class="content-block">About</h2>
+
+<p class="content-block dx-card responsive-paddings">Use this area to provide additional information.</p>

DXApp.TemplateKitProject/Pages/About.cshtml.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace DXApp.TemplateKitProject.Pages
+{
+    public class AboutModel : PageModel
+    {
+        public void OnGet()
+        {
+
+        }
+    }
+}

DXApp.TemplateKitProject/Pages/Error.cshtml

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+@page
+
+<h2 class="content-block">An error occurred while the server was processing your request.</h2>
+
+<div class="content-block dx-card responsive-paddings">
+    To display detailed information about the error, set the <strong>ASPNETCORE_ENVIRONMENT</strong> environment variable to <strong>Development</strong> and restart the app.
+    <br /><br />
+    <strong>The Development environment should not be enabled for deployed applications</strong> because it provides users access to exceptions that can contain sensitive information.
+</div>

DXApp.TemplateKitProject/Pages/Error.cshtml.cs

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+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using Microsoft.Extensions.Logging;
+
+namespace DXApp.TemplateKitProject.Pages
+{
+    [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
+    public class ErrorModel : PageModel
+    {
+        public void OnGet()
+        {
+        }
+    }
+}

DXApp.TemplateKitProject/Pages/Index.cshtml

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+@page
+@using DXApp.TemplateKitProject.Models
+
+<h2 class="content-block">Home</h2>
+
+@(Html.DevExtreme().DataGrid<SampleOrder>()
+    .ElementAttr(new { @class = "dx-card wide-card" })
+    .DataSource(d => d.Mvc().Controller("SampleData").LoadAction("Get").Key("OrderID"))
+    .ShowBorders(false)
+    .FilterRow(f => f.Visible(true))
+    .FocusedRowEnabled(true)
+    .FocusedRowIndex(0)
+    .ColumnAutoWidth(true)
+    .ColumnHidingEnabled(true)
+    .Columns(columns => {
+        columns.AddFor(m => m.OrderID);
+        columns.AddFor(m => m.OrderDate);
+        columns.AddFor(m => m.CustomerName);
+        columns.AddFor(m => m.ShipCountry);
+        columns.AddFor(m => m.ShipCity);
+    })
+    .Paging(p => p.PageSize(10))
+    .Pager(p => p
+        .ShowPageSizeSelector(true)
+        .AllowedPageSizes(new[] { 5, 10, 20 })
+        .ShowInfo(true)
+    )
+)

DXApp.TemplateKitProject/Pages/Index.cshtml.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace DXApp.TemplateKitProject.Pages
+{
+    public class IndexModel : PageModel
+    {
+        public void OnGet()
+        {
+
+        }
+    }
+}

DXApp.TemplateKitProject/Pages/Invoices/Upload.cshtml

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+@page
+@model DXApp.TemplateKitProject.Pages.Invoices.UploadModel
+@{
+    ViewData["Title"] = "PDF/A Upload";
+}
+
+<h2>PDF/A Rechnung hochladen</h2>
+
+<form method="post" enctype="multipart/form-data">
+    <div class="mb-3">
+        <label asp-for="PdfFile" class="form-label">PDF/A-Datei auswählen</label>
+        <input asp-for="PdfFile" type="file" class="form-control" accept=".pdf" />
+        <span asp-validation-for="PdfFile" class="text-danger"></span>
+    </div>
+    <button type="submit" class="btn btn-primary">Hochladen &amp; Analysieren</button>
+</form>
+
+@if (Model.ExtractionDone)
+{
+    <hr />
+    <h4>Ergebnis</h4>
+
+    @if (!string.IsNullOrEmpty(Model.ErrorMessage))
+    {
+        <div class="alert alert-danger">@Model.ErrorMessage</div>
+    }
+    else if (Model.Result == null || !Model.Result.HasAttachments)
+    {
+        <div class="alert alert-warning">Keine Anhänge in der PDF gefunden.</div>
+    }
+    else
+    {
+        <div class="alert @(Model.Result.HasZugferdXml ? "alert-success" : "alert-warning")">
+            @if (Model.Result.HasZugferdXml)
+            {
+                <strong>✔ ZUGFeRD/Factur-X XML gefunden:</strong>
+                <span>@Model.Result.ZugferdXmlAttachment!.OriginalFileName</span>
+            }
+            else
+            {
+                <strong>⚠ Kein ZUGFeRD-XML gefunden.</strong>
+            }
+        </div>
+
+        <table class="table table-sm table-bordered">
+            <thead class="table-light">
+                <tr>
+                    <th>Dateiname</th>
+                    <th>Größe</th>
+                    <th>ZUGFeRD?</th>
+                    <th>Gespeichert unter</th>
+                </tr>
+            </thead>
+            <tbody>
+                @foreach (var a in Model.Result.Attachments)
+                {
+                    <tr class="@(a.IsZugferdXml ? "table-success" : "")">
+                        <td>@a.OriginalFileName</td>
+                        <td>@($"{a.FileSizeBytes:N0}") Bytes</td>
+                        <td>@(a.IsZugferdXml ? "✔ Ja" : "Nein")</td>
+                        <td><small class="text-muted">@a.SavedFilePath</small></td>
+                    </tr>
+                }
+            </tbody>
+        </table>
+    }
+}

DXApp.TemplateKitProject/Pages/Invoices/Upload.cshtml.cs

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+using DXApp.TemplateKitProject.Models;
+using DXApp.TemplateKitProject.Services;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace DXApp.TemplateKitProject.Pages.Invoices;
+
+public class UploadModel(
+    PdfAttachmentExtractorService extractor,
+    ILogger<UploadModel> logger) : PageModel
+{
+    [BindProperty]
+    public IFormFile? PdfFile { get; set; }
+
+    public PdfExtractionResult? Result { get; private set; }
+    public bool ExtractionDone { get; private set; }
+    public string? ErrorMessage { get; private set; }
+
+    public void OnGet()
+    { }
+
+    public async Task<IActionResult> OnPostAsync()
+    {
+        if (PdfFile is null || PdfFile.Length == 0)
+        {
+            ModelState.AddModelError(nameof(PdfFile), "Bitte eine PDF-Datei auswählen.");
+            return Page();
+        }
+
+        if (!PdfFile.FileName.EndsWith(".pdf", StringComparison.OrdinalIgnoreCase))
+        {
+            ModelState.AddModelError(nameof(PdfFile), "Nur PDF-Dateien sind erlaubt.");
+            return Page();
+        }
+
+        ExtractionDone = true;
+
+        try
+        {
+            await using var stream = PdfFile.OpenReadStream();
+            Result = extractor.ExtractAttachments(stream, PdfFile.FileName);
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex, "Fehler beim Verarbeiten der Datei '{FileName}'.", PdfFile.FileName);
+            ErrorMessage = $"Fehler beim Verarbeiten der Datei: {ex.Message}";
+        }
+
+        return Page();
+    }
+}

DXApp.TemplateKitProject/Pages/Shared/_Layout.cshtml

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+<!DOCTYPE html>
+
+<html>
+<head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+    <title>DXApp.TemplateKitProject</title>
+    @* Custom theme with a color swatch *@
+    @* Docs: https://js.devexpress.com/DevExtreme/Guide/Themes_and_Styles/Predefined_Themes/#Color_Swatches *@
+    <link href="~/css/devextreme/dx.fluent.blue.light.css" rel="stylesheet" />
+    <link rel="stylesheet" href="~/css/Site.css" />
+    <script src="~/js/devextreme/jquery.js"></script>
+    <script src="~/js/devextreme/dx.all.js"></script>
+    <script src="~/js/devextreme/aspnet/dx.aspnet.mvc.js"></script>
+    <script src="~/js/devextreme/aspnet/dx.aspnet.data.js"></script>
+</head>
+
+<body class="dx-viewport">
+    <div id="app-side-nav-outer-toolbar">
+        <div class="layout-header">
+            @(Html.DevExtreme().Toolbar()
+                .Items(items => {
+                    items.Add()
+                        .Widget(w => w
+                            .Button()
+                            .Icon("menu")
+                            .OnClick("DevExtremeAspNetCoreAppMatRazorPages.onMenuButtonClick")
+                        )
+                        .Location(ToolbarItemLocation.Before)
+                        .CssClass("menu-button");
+                    items.Add()
+                        .Html("<div>DXApp.TemplateKitProject</div>")
+                        .Location(ToolbarItemLocation.Before)
+                        .CssClass("header-title");
+                })
+            )
+        </div>
+        <div class="layout-body layout-body-hidden">
+            @(Html.DevExtreme().Drawer()
+                .ID("layout-drawer")
+                .Position(DrawerPosition.Left)
+                .Opened(new JS("DevExtremeAspNetCoreAppMatRazorPages.restoreDrawerOpened()"))
+                .Content(@<text>
+                    <div id="layout-drawer-scrollview" class="with-footer">
+                        <div class="content">
+                            @RenderBody()
+                        </div>
+                        <div>
+                            <div class="content-footer">
+                                <div id="footer">
+                                    Copyright (c) 2000-@DateTime.Now.Year Developer Express Inc.
+                                    <br />
+                                    All trademarks or registered trademarks are property of their respective owners.
+                                </div>
+                            </div>
+                        </div>
+                    </div>
+                </text>)
+                .Template(new TemplateName("navigation-menu"))
+            )
+        </div>
+    </div>
+
+    @using(Html.DevExtreme().NamedTemplate("navigation-menu")) {
+        <div class="menu-container dx-swatch-additional">
+
+            @functions{
+                string GetUrl(string pageName) => Url.Page(pageName);
+                string GetCurrentUrl() => Url.Page(ViewContext.RouteData.Values["page"].ToString());
+                bool IsCurrentUrl(string pageName) => GetUrl(pageName) == GetCurrentUrl();
+            }
+
+            @(Html.DevExtreme().TreeView()
+                .Items(items =>
+                {
+                    items.Add()
+                        .Text("Home")
+                        .Icon("home")
+                        .Option("path", GetUrl("/Index"))
+                        .Selected(IsCurrentUrl("/Index"));
+
+                    items.Add()
+                        .Text("About")
+                        .Icon("info")
+                        .Option("path", GetUrl("/About"))
+                        .Selected(IsCurrentUrl("/About"));
+                })
+                .ExpandEvent(TreeViewExpandEvent.Click)
+                .SelectionMode(NavSelectionMode.Single)
+                .SelectedExpr("selected")
+                .FocusStateEnabled(false)
+                .Width(250)
+                .OnItemClick("DevExtremeAspNetCoreAppMatRazorPages.onTreeViewItemClick")
+            )
+
+        </div>
+    }
+
+    <script>
+
+        var DevExtremeAspNetCoreAppMatRazorPages = (function() {
+
+            var DRAWER_OPENED_KEY = "DevExtremeAspNetCoreAppMatRazorPages-drawer-opened";
+
+            var breakpoints = {
+                xSmallMedia: window.matchMedia("(max-width: 599.99px)"),
+                smallMedia: window.matchMedia("(min-width: 600px) and (max-width: 959.99px)"),
+                mediumMedia: window.matchMedia("(min-width: 960px) and (max-width: 1279.99px)"),
+                largeMedia: window.matchMedia("(min-width: 1280px)")
+            };
+
+            function getDrawer() {
+                return $("#layout-drawer").dxDrawer("instance");
+            }
+
+            function restoreDrawerOpened() {
+                var isLarge = breakpoints.largeMedia.matches;
+                if(!isLarge)
+                    return false;
+
+                var state = sessionStorage.getItem(DRAWER_OPENED_KEY);
+                if(state === null)
+                    return isLarge;
+
+                return state === "true";
+            }
+
+            function saveDrawerOpened() {
+                sessionStorage.setItem(DRAWER_OPENED_KEY, getDrawer().option("opened"));
+            }
+
+            function updateDrawer() {
+                var isXSmall = breakpoints.xSmallMedia.matches,
+                    isLarge = breakpoints.largeMedia.matches;
+
+                getDrawer().option({
+                    openedStateMode: isLarge ? "shrink" : "overlap",
+                    revealMode: isXSmall ? "slide" : "expand",
+                    minSize: isXSmall ? 0 : 60,
+                    shading: !isLarge,
+                });
+            }
+
+            function init() {
+                $("#layout-drawer-scrollview").dxScrollView({ direction: "vertical" });
+
+                $.each(breakpoints, function(_, size) {
+                    size.addListener(function(e) {
+                        if(e.matches)
+                            updateDrawer();
+                    });
+                });
+
+                updateDrawer();
+
+                $('.layout-body').removeClass('layout-body-hidden');
+            }
+
+            function navigate(url, delay) {
+                if(url)
+                    setTimeout(function() { location.href = url }, delay);
+            }
+
+            function onMenuButtonClick() {
+                getDrawer().toggle();
+                saveDrawerOpened();
+            }
+
+            function onTreeViewItemClick(e) {
+                var drawer = getDrawer();
+                var savedOpened = restoreDrawerOpened();
+                var actualOpened = drawer.option("opened");
+
+                if(!actualOpened) {
+                    drawer.show();
+                } else {
+                    var willHide = !savedOpened || !breakpoints.largeMedia.matches;
+                    var willNavigate = !e.itemData.selected;
+
+                    if(willHide)
+                        drawer.hide();
+
+                    if(willNavigate)
+                        navigate(e.itemData.path, willHide ? 400 : 0);
+                }
+            }
+
+            return {
+                init: init,
+                restoreDrawerOpened: restoreDrawerOpened,
+                onMenuButtonClick: onMenuButtonClick,
+                onTreeViewItemClick: onTreeViewItemClick
+            };
+        })();
+
+        document.addEventListener("DOMContentLoaded", function documentReady() {
+            this.removeEventListener("DOMContentLoaded", documentReady);
+            DevExtremeAspNetCoreAppMatRazorPages.init();
+        });
+    </script>
+</body>
+
+</html>

DXApp.TemplateKitProject/Pages/_ViewImports.cshtml

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+@using DXApp.TemplateKitProject
+@namespace DXApp.TemplateKitProject.Pages
+@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+@using DevExtreme.AspNet.Mvc

DXApp.TemplateKitProject/Pages/_ViewStart.cshtml

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+@{
+    Layout = "_Layout";
+}