The default encryption scheme of Word and Excel has the same default as Windows password hashes, it is predictible (there is no salt or randomness). We have a product that cracks a Word or Excel document in minutes, whatever the password (any length or complexity) What we crack is not the password but the resulting 40 bit key that is used to encrypt the document. I coined the name rainbow table in my research paper presented at Crypto 2003. I could get you a evaluation version if you wanted to test (would have to send you a DVD with the 4GB of tables). Alternatively I could crack a few documents for you.”]
Source: https://www.csoonline.com/article/2631669/phillip-oechslin-responds-to-my-rainbow-table-column.html