To encrypt and password‑protect a file, use File > Encrypt, specify a password of at least six characters, and choose an encryption algorithm.

When a workbook is encrypted, the “shield” toolbar button turns green.

Note: GS-Calc uses standard ODF encryption and encrypts all workbook content (tables, styles, charts, images, settings, etc.). However, names of inserted images remain unencrypted inside *.ods files.