I want to combine two PDF files. I try to combine them (Create PDF-->From Multiple Files), but when I try to add the PDF I actually created myself, it tells me that it is protected. I have checked it, and it has no security settings, so I don't know why it won't combine. The other file, that wasn't even created by me (but my company in the past), has no problem combining with other files. Does anyone know why this is?