This is the heavy-duty lock. When you set an "Open" password, Excel encrypts the entire file using AES-128 or AES-256 (Advanced Encryption Standard). Without the correct key, the data is mathematically scrambled into gibberish.

If you can open the file but cannot edit cells or unhide sheets, you do not need LostMyPass.

This is a flimsy lock. It prevents users from editing cells, hiding sheets, or moving structures. Crucially, this is NOT encryption. It’s a simple flag in the XML code.

Why this matters for LostMyPass: LostMyPass specializes in Type A (the hard one). If you search for "lostmypass ms excel password recovery best," you are likely dealing with an encrypted file that refuses to open at all.