In the last 3 months I have continually ran into a problem where many of the PDFs on my site keep coming up in the not found area of webmaster tools. These are valid links and I can load them every time I click them. I was wondering does Google bot have a problem with PDFs? Like is there a way I need to host or optimize them to get them to not error. This doesn't happen for all of my pdfs but a good amount.