>>>My goal is to deliver the document without a hacker getting the information. I think your suggestion of using the ZIP with a password is a good one. I will try it with the dropbox.
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>Don't be surprised if Dropbox protests at the encrypted file or even blacklists it. Gmail can do that too, as can customer firewalls. We've had best success attaching files to our online support system for customers to log in and download.
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>I know you don't want to install stuff- but if you use native Windows zipping, it uses the old zipcrypto that's easily cracked in seconds, rather than AES-256 that's difficult to crack.
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>I have not checked Excel encryption recently but my experience of Office encryption always was that it's easily overcome.
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>Your best bet is to install the same 3rd party tool at both ends. Options for Windows and Mac include 7zip as others have noted. Veracrypt also works on both and has features allowing embedded encrypted volumes that are difficult to detect let alone hack, but Veracrypt needs a little more preparation than 7zip that can be added to Explorer rightclick. Others recommend Truecrypt, but it has proven hack vectors that won't be fixed. Veracrypt is a smart fork from it IMHO.
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>Finally, you need to send the password separately from the link or file so that (hopefully) it doesn't traverse the same snooping server/s. Or phone or text them the password- txt isn't secure, but it doesn't traverse the same servers as the file or link.

Why are you saying that text isn't secure? IIRC, the FBI was asking Apple to help getting messages from the San Bernardino terrorist's cell phone because they could not get in any other way.