Mac PDF files not readable on PC

I am constantly getting messages from my PC friends that the photoshop files I create and then convert to either pdf or jpg are not readable on their pc. Sometimes the files are split into two files (one very small and the other large) with the same name. The larger file is usually able to be opened.

What can I do to make my proofs easier to read for pc users? This has gotten frustrating.

Thanks for your help.