Your comments

Hi Robert, you are correct I am retrieving attachments with MIME Type application/pdf. 

Hi Robert, I tried to replicate this error in 3 different environment, but it worked for me in all of them. Can you maybe inspect browser console to see if there are any errors?

Hi Robert,

Do you have the problem with previewing PDFs in full screen mode as well? Or it just doesn't show you PDF image placeholder? Also can you tell me the size of that PDF file? I will try to replicate this error on my side and will try to help you.

Hi Robert,

You can check out my Attachment Gallery Control - it supports viewing PDF files.