I looked into the helper.php file but I don't think this would work unless I removed all other references to .jpg and .gif while renaming PNG to PDF. Otherwise just renaming PNG leaves us with the option to still accept these last two as valid formats.
Using the Convert to PNG which is now convert to PDF fails as the code just renames the image file that was uploaded with a PDF extension.
Thanks for the suggestions. I could not even get the form validator to throw an error when the file uploading were the wrong format. It completely ignored the extension. Tried on blur and on submit????
I tried checking on server file name and file extension from the WA Upload bindings. Any suggestion here?