>>>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.

As yes very important to use the right encryption level when zipping!!

>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 lets you hide embedded volumes that are almost impossible to detect let alone hack, but it needs a little more preparation than 7zip that can be added to Explorer right click. Truecrypt used to be popular until in 2015 "critical vulnerabilities" were reported that won't be fixed. I'd say 7zip is most convenient and accessible.
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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.