XTML files are Uncommon Files primarily associated with XML4web Virtual HTML File (Altair Communications Corporation) These are for displaying webpages.
The fastest and easiest way to open your XTML file is to double-click it. This allows the intelligence of Windows to decide the correct software application to open your XTML file.
In the case that your XTML file doesn’t open, it is highly likely that you do not have the correct software application installed on your PC to view or edit XTML file extensions.
If your PC opens the XTML file, but it’s the wrong application, you’ll need to change your Windows registry file association settings. In other words, Windows is associating XTML file extensions with the wrong software program.