Saved PDF files are unreadable

I want to use my iXpand to save created PDF files at my iOS devices and print them at our printer at work.
I tried many apps (Word, PDF Expert, Mail app, Notability, …) but on iXpand the saved files are unreadable.
Sometimes I can open them but they have illustration errors or are completely empty.

The printer won’t print any of these files.

What can I do?

if you can provide more info on how you are creating the pdf files and how they are being transferred to the iXpand drive that will be helpful. 

also can the files be opened on a computer? after you create the pdf can it be emailed and opened normally? Can you print the pdf from email? Im interested to see if the issue occurs during the creation of the file or when it is saved to the iXpand.