PDF files do not open

Hello everyone!
EmClient version 7.2.50008.0.
PDF files open with an error if the incoming server is configured as IMAP. If the incoming server is configured as POP, then everything is ok. But it is not convenient for us to use POP.
Version 8.2.1721.0 does not have this problem.
License terms do not allow updating 7.2.50008.0 to 8.2.1721.0. What should we do? I have 200 users, and this is a big problem.