Use the Form creator in Adobe Acrobat. I'm using Adobe Acrobat 9 but it works in lower versions as well.

Select Forms > Create new Form
Select 'Start with an Electronic Document'
follow the prompts.
When asked to identify fields, select 'Run Auto Field Detection'. This often works better.
Once complete, Adobe LiveCycle will open up.
Here you can modify your fields and edit its options.

For more info, read up on the help for Adobe LiveCycle.

*LiveCycle should be installed already with the Adobe Creative Suite.

@Colin: Why does it have to be a PDF if it needs to be editable? Word processors allow forms with fixed as well as editable contents.

BTW, OpenOffice.org offers a plugin to edit PDFs in OOo Draw.

@xil3: It cannot be safely assumed ;-) that Colin's client is willing to buy CS for that purpose. Field contents in PDF forms cannot be saved with Acrobat Reader.

Andreas

There's a lot out there on this. A coulple of threads:

http://www.dslreports.com/forum/r21288689-Make-PDF-editable
http://roobaroo.net/2006/06/30/create-an-editable-pdf-document/
http://www.hardwaregeeks.com/board/showthread.php?t=18172

seems you can use the form tools to make text fields (haven't tried myself though)

good luck!

Adobe Acrobat lets you make changes to the text of a PDF, as long as you embed the fonts AND have these fonts loaded on your computer. But the editing is limited to single lines (i.e., it would be tedious and painful to edit an entire paragraph!). Is this what your client is asking for? (It's not the same as making a form with fields to fill in.) Your client would have to own Acrobat, not Reader, to be able to edit the PDF.

@Fontgrube only the designer needs to have the CS suite.
once the form is created with fields, that form is usable by anyone with reader.
The contents will stay with the file when the file is saved.

Think to when you are downloading a Passport application.
You can fill out digital fields and save the document with all fields saved.

To disable editing, you just have to secure the document so no one can change the content of the fields.

But whatever works best.

Thanks everyone for all the info — my client ended up deciding that I'll stick to making the changes :P