Can I change the title of my FolderBrowserDialog?

The simple answer is that you can't. The dialog displays using the standard title for a folder browser style dialog on Windows. The best option is to ensure that you have meaningful descriptive text by setting the Description property.

Even if you were to use P/Invoke to call the SHBrowseForFolder Win32 API function directly, the only option you still can't change the actual title of the dialog. You can set the lpszTitle field of the BROWSEINFO structure, which is

A pointer to a null-terminated string that is displayed above the tree view control in the dialog box. This string can be used to specify instructions to the user.

You can't if you use the class FolderBrowserDialog directly. But I read somewhere that it could be possible to change the title with P/Invoke and sending WM_SETTEXT message.

In my opinion, it is not worth the pain. Just use the property Description to add the information:

FolderBrowserDialog dlg = new FolderBrowserDialog();
dlg.Description = "Select the document folder";