How does “Recycle master recycle bin” app recovering deleted files ?

There are many apps that recovers deleted data(images, video, PDF) i.e Disk digger , Dumpster e.t.c and these apps also ask for root , but here i want to know the process/methodology of simple recovering of files which are accidentally deleted.

In Recycle master recycle bin what have they tried to recover files using no root and it does provide the deleted files in app list view.

So to perform such task what i have to do in my app.

1) Are they implementing their own file manager by over riding/uninstall the default file manager so that user when ever open files it must interact with their file manager. If so then how to override default file manager ?

2) Are they over riding system calls to force operating system functionality?

3) Or there is some thing else?

Recovering evince session in Ubuntu 16.04

How can I recover documents which were open in Evince prior to a system crash in Ubuntu 16.04? Ideally, I would like to find a list of files which were open just before the crash. At the least, I would like to find some sort of history.

I did a crash simulation on another computer and found out that after opening evince after an unexpected shutdown it does offer a list of “recently viewed filed”. Where is this list of recently opened (in Evince) files stored in Ubuntu 16.04? Can I also extract the dates when each document was opened or at least the order in which they had been opened?

I tried using gvfs-info, but the result produced looked rather unsystematic: it both showed files which were opened a long time ago, but never recently, and did not show files which were opened during the crashed session. Is there a more efficient way of using gvfs for my purpose?