When my work partner opens certain PDF files emailed to him through his outlook app, those PDF files become corrupt and will not open with any application. If he forwards that email with the PDF to others, the PDF remains corrupt.
BUT, but he accesses that same PDF through OWA he can open it without issue, and when he forwards that email with the PDF in it to anyone else through OWA the PDF can open without issue.
What could be happening with his outlook application that is causing these PDF's to become corrupted?
1. Check the file size first. Are they the same or is the corrupted one really small compared to the working one?
2. Next, use a text editor like notepad to open up the PDF that doesn't work and see if the content looks like a normal PDF (you can do the same thing with the working PDF to see what it -should- look like) or if the content of the corrupted PDF is actually something like web page / HTML or an error message or something. (My guess is that you'll see something that clearly isn't a PDF).
3. If the beginning of the corrupted file looks like a normal PDF (looks like the beginning of the working PDF) then scroll down to to the very end and see if there is anything at the bottom that might indicate an error or perhaps it was cut off. If it was cut off, then the exact size (in bytes) of the corrupted PDF might be very important.
4. Finally, if saving the files to the local hard drive results in two PDFs that are identical and both of them open up correctly, then that might indicate it's just a problem with the embedded viewer / plugin within desktop Outlook.