Thank you, everybody, for your replies.
Since my posts, I've had two wonderful surprises.
The first: Acrobat Standard now only costs $300 instead of the $900 or so back when I got Acrobat 7.0.
The second: I used Acrobat for my freelance editing work. After looking at Adobe's product comparison page, I realized the free Adobe Reader now has all the commenting tools I need for my work. I just tried it out, and it'll work fine.
Thank you, Adobe, for Reader's free commenting tools--although you would have saved me a lot of time if you hadn't made me try downloading A7 by Internet, then phone, then sending me a link, then say you didn't know why I couldn't use the link and have to find out from the forum that I couldn't easily install it on a post-XP computer! But I send a big, unqualified thank you to you community forum members for your replies.
Best, Marc