How can I securely edit an Office file that I downloaded from the Internet?

Question

When I open an Office file such as a Word file that was downloaded from the internet, it warns me that it might not be safe to edit unless I trust the file source, but what if I actually need the file and need to edit it?

Can I remove whatever it is that can make it dangerous?

In what way can I check that the file is not a threat?

Answer 1

While in read-only protected mode, select all text, and copy/paste into a new document.

The text of the document is not the threat but any macros and programming behind the document are threats. So, if you only need the text, copy that.

But, it is often not that simple. Some documents (like Excel) require macros and some programming to make them useful. At that point, you need to either:

• open the document in the most up-to-date document reader available
• open the document in a reader that is not the most common and targetted reader (something other than MS Office, like LibreOffice)
• open and edit the document in on online reader (like Office 365)
• open the document in a sandbox (like a Virtual Machine) that can limit the impact if the document is going to do something malicious

These options do not check that there is no threat, but it severely limits what impact the threat may have.

Answer 2

There is no 100% safe to open a document, but a couple things to add to previous answers.

• upload the file to virustotal.com and see if it comes back malicious, if it does, don't open it!
• Open the file in a Virtual Machine running office