What to find out who lasted updated a form template?
end user: “My InfoPath form has stopped working!”
me: oh, did anyone make a change to the form?
end user: “umm, not that I know of?!?!”
Open the site using SharePoint Designer.
In the left side of Designer, click on All Files.
From there, click on the Library name you are wanting to inspect.
The Library will now be open in your main panel / window.
Open the Form folder.
In there you should see a template.xsn file. *your template might be named something different, but look for the file with a Type of xsn.*
The Modified By column will show you the last user that made any changes to the template.