Is the form supposed to be in PDF format? I ask because the message implies that it isn't, or it it is corrupted.
It is either an invalid PDF, or the PDF was corrupted during the download.
If this is a public document, can you post a link to it?
it is meant to be in a PDF format and from the infomation i was given to fix the issue it seems a common problem for majority
this is a print screen on the national Security Vetting site and is only accesible if i'm correct from someone who is giving infomation to set up a secure account with the government .i can post you a link but you might not be able to access the site ( you could if youhave already registered )
link to the site : https://www.nsv.mod.uk/Login.aspx?ReturnUrl=%2f