Unfortunately, no. Word Online can’t encrypt a document with a password, and it can’t open documents encrypted with a password.
However, if you have the desktop version of Word, you can use it to password-protect your document. Click Open in Word to open your document in the desktop version of Word.
After opening your document in Word, follow the instructions in Password-protect your document. Then, press Ctrl+S to save your document to its original location. After closing your document, you’ll need to use the Word desktop program to open it again.
Tip: The Office Web Apps are updated all the time with new features. Visit the Office Online blog for the latest news and announcements.