filling out a pdf form

Are there really form fields present or does the PDF just have an underline where a form field could be placed?

You should be able to 'highlight' the form fields either through an option on the purple information bar or setting Reader's preferences ("Edit => Preferences => Forms" or " + K") if there are form fields present.

I think you're right, they're just lines...
What do I need to do in order to fill in the lines?? How do I turn them into "form fields"??

You would need a full version of Acrobat 9 or the creator of the form would need to add form fields or enable commenting for Reader.

When your program is open, go to the "Help" menu option and select the "About ...". A pop-up widow will open and show your product and full version number.

If you have version 6 of Acrobat, you will need the Professional variation to be able to create or edit form fields.

Yes, since you do not have Acrobat.

To add form fields you will need either Acrobat version 9 Standard or Professional. Standard has very limited form creation and JavaScript programing ability. Professional provides full Acrobat form programing and with the Windows version you will also have LiveCycle Designer.

Adobe has a 30 free day trial version of Acrobat 9 available for download.