After a bit of searching through your forums, I was able to find this post.
https://firstgenfirebird.org/forums/ubbthreads.php?ubb=showflat&Number=324127

I assume this is the post you were having issues with?

Im able to view the PDF inline just fine.

My browser's user-agent string is
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:69.0) Gecko/20100101 Firefox/69.0

[Linked Image]

current developer of UBB.threads php forum software
current release: UBB.threads 8.0.1 // wip: UBB.threads 8.1.0
isaac @ id242.com // my forum @ CelicaHobby.com