Hello, guys!
Basically, I need to be sure if Calc security protections are really impossible to break.
Is there a way to break password protections applied in a Calc plan? ou Calc file?
My apologies if this question is too basic or fool…
There is encyption which requires the correct password before loading the document. This can be accepted as safe.
Once the document is loaded, you can do anything with it. All the protections on document level are no more than child-proof measures against accidental editing.
Right. Only the password protected document encryption is secure (down to the weakness of the password used of course). Everything else is just cosmetic workflow flags and can be removed with a bit of knowledge and craftsmanship; in both ODF .ods and OOXML .xlsx (and legacy binary .xls) file formats.
See also Frequently asked questions - Calc - The Document Foundation Wiki .