There are 2 project backup functions:

Backup Project - Creates a single file (.tpx) with project information (takeoff), but it does NOT save the drawing files. To restore this type of backup, make sure the .tpx file is in a folder with all the drawing files. Navigate to the file and double click it.

Backup and Zip Project - creates a single file (.tpxzip) with both the project information and the drawings. To restore this type of backup, make sure the .tpxzip file is in a folder by itself. Navigate to the file and double click it.