Update configuration code to use the new configuration keys.

ConfForm.cs

@@ -96,7 +96,15 @@ namespace PDF_Merge
 
         private void outPathBtn_Click(object sender, EventArgs e)
         {
-            using (var OutPathPicker = new OpenFileDialog()) { }
+            using (var OutPathPicker = new FolderBrowserDialog())
+            {
+                OutPathPicker.RootFolder = Environment.SpecialFolder.Desktop;
+                if (OutPathPicker.ShowDialog() == DialogResult.OK)
+                {
+                    var OutPath = OutPathPicker.SelectedPath;
+                    outputBox.Text = OutPath;
+                }
+            }
         }
     }
 }