Do you have to have Microsoft office for Documents and other programs?

No you do not. It is true that Microsoft Office is an excellent group of apps. But there are other apps which can do essentially the same things, although there are some differences. Those other apps are able to open Microsoft files and then, after making changes (in their native formats) they can save the result in a Microsoft format. Sometimes formatting changes may be unable to be saved, however. It gets down to how willing person is to deal with the conversion requirements when interacting with other people who are using Office apps.

That's two different questions as your topic title and body text have nothing to do with each other.

If you can't read the code on the gift card, well, then that's a problem as you need to be able to read the entire thing in order to redeem it.

No, you don't have to have MS Office to read or write Word, PowerPoint or Excel documents. You can use Apple's free (but very lackluster) Pages, Numbers and Keynote apps. There's also much better choices with the free LibreOffice, or the much less expensive Softmaker Office suite. They also have a free version, which is mostly the same but lacks a spellcheck feature.

The main reason to have Office is if your company uses it as its standard apps. Often in that case, you can get a free (or discounted) version of office through them, or just use Safari and log into your Office 365 account from there.

Thanks