How to recover the file deleted?

[饽饽饽饽饽]

Hi,
My friend have used the device delete a PDF note which is very important. I look through the Internet still have no idea how to help her recover the file.
She has done nothing since deleted the file.
Do you have any idea?
( your tool is very magic, think you must be an expert in Dpt-Rp1's file system

Thanks a lot!