Saved changes in PDF file are lost

Hello,

One of our users has highlighted lots of text in a PDF file using the last version of Acrobat Reader DC on Windows 10 during multiple hours and saved the PDF often in between. However she did not close the PDF file and had not logged out, during the night her compute rebooted automatically.

The day after this all her changes are lost and were not saved to the PDF file. The autosave feature was on and during the night a tmp file was present in the AutoSave AppData folder however it is not possible to recover the last version of the PDF using this file. The tmp file now is not present anymore but i could recover it from a backup during the night.

About what is noted above i have two questions:

* How is is possible that the changes had not been saved although she saved the file often? How can she prevent that the same happens again in the future? 

* Is there a possibility to recover the latest version of the file and how is this done?

Thanks in advance.

A System Administrator