How could I save a file from Solidworks 2020 to a 2016 version, for example? Can I do this?
3 Answers

You cannot save "back" current solidworks files to an old version. You can, however, save "up" from an old solidworks version to a more current version.
The best way to manage the issue is to take your solidworks 2020 files and save them off in a parasolid x_T, STEP, IGES, etc. Then import that file version into solidworks 2016.
You sill not be able to manipulate geometry, but you will be able to verify geometry either in sketches (in the model) or by creating a drawing and dimension to object lines in the drawing.
It is very likely that you will need to remodel the part completely in solidworks 2016, but having the imported file enables you to know exacting dimensions.