Cannot open PDF file which was working before in galaxy tab s6

[anh11101997]

Can anyone help me fix my problem related to galaxy tab s6, please? 
There are some PDF files that I cannot open anymore. I used to use the write-on PDF application to note on them, but now it is not working. I also tried with other applications like adobe, gg drive pdf, etc., but still have the same result. It shows something like an unrecognized file format or DRM protected. 
I really appreciate any help you can provide.
#tabs6 

[INTRASERVER]

Looks more like this pdf is signed to one person device. You need to register device from ther you downloaded. It is very close like to iTunes DRM.

[anh11101997]

Actually, it is not only happening to 1 file but many other files are also broken. 

[INTRASERVER]

I'm interested to know if you open this file on computer. Just transfer from tablet to computer.

[BlackOlive]

Urgh! This happens to me all the time too - same exact message. I haven't found a solution yet.

For anyone interested in this problem, all I've used the write-on PDF app for is the sudoku monster from the Sunday paper. Initially I was testing the app to see if I could use it for real work. Now that's all I use it for because it's locked me out of 4 files so far.

All four are PDFs I printed to PDF from an image. The image was taken with this device's camera. At no time have those files gone to any other device except when I sent a locked file to my laptop to try the software I have there. No dice. It only ever happens to a PDF I've worked on for a while, never with a new file. Annoying with a difficult puzzle, potentially devastating for important paperwork.

This problem is 100% local to my Tab S6 running android version 11.

[Members_IcwDBH1]

Same here ! Believable,

The error happened when is editing then try to save but there is no Internet. 

[saizal]

I faced the same issue with my Samsung s7 fe. To open, I transfer/send the corrupted document to my google drive and open using an alternative pdf reader such as Foxit pdf reader.

[Members_fKeVm78]

Hi, did you find a way to recover your files? i have the same problem with my S7 fe, and nothing seem to work for me, i lost all my university files with my notes on my tab !