From The Document Foundation Wiki
How to retrieve a document ?
- It is almost mandatory to copy the file from the backup folder to another folder. This is for two reasons:
- The .bak extension is not by default associated to LibreOffice. A double click on the file name will lead to a prompt asking you which program to use to open it. It is better to copy to another file to rename the document with its original extension (odt, ods...).
- Opening and modifying the backup copy within the backup folder will display an error during saving because, in the case of a modified document, LibreOffice is trying to create a backup copy with the same name in the same folder...