I would check the pdf file itself in case its corrupted as this sometimes happens for whatever reason
If you are getting the same problem with all pdf's then it may be a problem with Est as there should be no reason why it wont import
try importing something else like a dwg or a dxf to see if that works and it may indicate where the issue lies either with the file or the software
It is not the pdf file. What is unusual is I have .est installed on a desktop and then a company server. The server file will not import underlays, however my desktop imports them just fine. My workaround is to create the est file in my desktop est and put in all the underlays I need and then copy and paste the file into the server and open it in the server. The underlay shows up just fine then. ( I can't use the desktop est for other reasons)
The only difference is the company server doesn't have the advanced acrobat reader software like my desktop does, but I don't think that should make a difference.
Sounds like a server issue causing this and I am unfamiliar with the software being installed on a server
I have mine installed on desktop but database on the server and never had any similar problems
sorry not much help