What a password on a Word or Excel file actually protects
Office offers two kinds of password, and they are not the same thing. One encrypts the file so nobody can read it without the password. The other only asks the program to stop people editing — and anyone with the file can take it off. Knowing which one you set matters more than how long the password is.
26 September 2026 · 5 min read
Two kinds of password
- A password to open. File → Info → Protect Document (Protect Workbook, Protect Presentation) → Encrypt with Password. The whole file is encrypted. Without the password there is nothing to read — not the words, not the pictures, not the list of sheets.
- A password to change. Review → Restrict Editing in Word, Protect Sheet and Protect Workbook in Excel. The file is not encrypted at all. It carries a setting, and a hash of the password, asking the program to refuse edits. Anyone can open it and read every word.
How strong the encryption is
Since Office 2013, Encrypt with Password uses AES with a 256-bit key, and turns the password into that key through 100,000 rounds of SHA-512 with a random salt — a deliberately slow step that makes guessing passwords expensive. The file also carries a check value, so one that was altered after it was encrypted is refused rather than opened as garbage. The encryption is strong; the weak part is the password you choose.
Two practical consequences. A long passphrase is worth far more than a clever short password, because guessing is the only practical attack. And there is no recovery: nobody, including Microsoft, can open the file for you if the password is lost. Keep a record of it somewhere safe.
The old binary formats are a different story. A .doc or .xls saved by Office 97–2003 with a password used much weaker encryption, and tools that break it are freely available. If a file matters, save it as .docx or .xlsx before protecting it.
Why an editing password is not security
A .docx or .xlsx is a ZIP of XML parts. Restrict Editing and sheet protection are one element in one of those parts — w:documentProtection in a document’s settings, sheetProtection in a worksheet — naming what is locked and holding a hash of the password. The content itself is untouched, readable XML. Remove that element and the protection is gone, and some programs simply ignore it.
That is not a flaw; it is what the feature is for. It stops accidental edits to a form or a finished report, and it keeps colleagues to the cells they are meant to fill in. It is not for keeping anything secret. If the contents are confidential, encrypt the file as well.
Which one to use
- Confidential contents, or a file travelling by email or on a USB stick: Encrypt with Password.
- A form or template where people should fill in some parts and not others: Restrict Editing or Protect Sheet, with or without a password.
- Both at once is fine: an encrypted file can also have protected sheets.
And send the password by a different route from the file — a phone call or a text message, not the next email.
Our own product, disclosed
Where our own software comes into this
Since version 1.27, Rutba Word, Worksheets and Presentation open files encrypted by Office — both the current scheme and Office 2007’s — and Info → Encrypt with Password saves them encrypted as Office 2013 and later do: AES-256, SHA-512, 100,000 rounds. Restrict Editing, Protect Sheet and Protect Workbook are written as Office writes them, too. The password is held only in memory while the file is open, and the copy kept every half minute in case of a crash is encrypted with it.
Related
How to check a Word, Excel or PowerPoint file for accessibility
Every major office suite now has a checker, and each catches the same handful of problems: pictures with no description, headings that are only bold text, tables with no header row, colours too pale to read, slides with no title. Here is what they check, what they cannot, and how to fix what they find.
What is actually inside a .docx file
Rename it to .zip and look. Understanding the parts explains almost everything about why documents behave the way they do between programs — and lets you fix a corrupt file by hand.
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