add MergeDocumentException

EnvelopeGenerator.Application/Exceptions/MergeDocumentException.cs

@@ -0,0 +1,22 @@
+namespace EnvelopeGenerator.Application.Exceptions;
+
+/// <summary>
+/// 
+/// </summary>
+public class MergeDocumentException : ApplicationException
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="message"></param>
+    public MergeDocumentException(string message)
+        : base(message) { }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="message"></param>
+    /// <param name="innerException"></param>
+    public MergeDocumentException(string message, Exception innerException)
+        : base(message, innerException) { }
+}