Am I missing something?

You don't mention which version of PDF you are using... But with PDF 8 the creator of a PDF document/form can open the ADVANCED drop down menu and select the entry that says something like "Enable User Rights"... Once you have done this and saved your document your users will be able to edit any field.

Jim,

2 things about this:

1) if the pdf you're sending is a scan or graphically based, then your ability to edit text is out of scope. Text embellished as a graphic won't give you the opportunity to edit the content. If the pdf was created using a layout application (such as InDesign or even Word), then the text from those app's should enable you to edit text.
2) Assuming that your partner also has the full version of Acrobat (ie: Professional), then he/she should have tools available to edit text.

That said, however, the big caveat here depends on how your doc was set up and again, if what we're dealing with here is an image, then no further editing can happen.

Rob