Try to open file if hyper link does not contain a valid URL

src/Markdowser/Commands/HyperlinkCommand.cs

@@ -1,6 +1,8 @@
 using Markdowser.Utilities;
 
 using System;
+using System.Diagnostics;
+using System.IO;
 using System.Windows.Input;
 
 namespace Markdowser.Commands;
@@ -32,6 +34,22 @@ public class HyperlinkCommand : ICommand
             {
                 GlobalState.CurrentTabState.Url = new Uri(new Uri(GlobalState.CurrentTabState.Url), url).ToString();
             }
+            else if (File.Exists(url))
+            {
+                ProcessStartInfo processStartInfo = new()
+                {
+                    FileName = url,
+                    UseShellExecute = true
+                };
+                try
+                {
+                    _ = Process.Start(processStartInfo);
+                }
+                catch (Exception ex)
+                {
+                    GlobalState.Logger.LogError(ex.Message);
+                }
+            }
             else
             {
                 GlobalState.Logger.LogDebug($"Invalid URL: {url}");