How to recover disappeared PDFs on my iPad 10th generation?

All my PDF edited with pencil ( hardwork site measurement for 3-4 day) .. save in "On My Ipad - in Sub folder) .... after few days.. maybe 1 week.... That Sub Folder Completely disappeared without any error, without being detected, without any sign of where it went.

It's really disappointing.

On the Official Apple website, No Helping. they closed the complaint thread from the user after a few comments... you can check here PDF suddenly disappeared - Apple Community

Now I have to bear the shame and have to redo all the work that should have been completed.

Be careful everyone... this error should not happen and it is very difficult to accept. Because it is clearly an error of the iPad system itself. The iPad I am using is a 10th Gen iPad.

[Re-Titled by Moderator]

Original Title: PDF Completely disappeared without any error, without being detected, without any sign of where it went.