How do you fill out a form attached to an email?

If you have an electronic camera, you can print the form, fill it in, photograph it, and send it as an attachment to an e-mail.

Quite a hassle.

I would be tempted to phone or e-mail the person who sent it and ask them to re-send it in a format that can be filled in on the computer.

And no, Microsoft Office does not have an option that will help.

As Gymstagran says, it's the easiest option, if you are not too office oriented.

I've found that if you "save" the file you can then fill in the form and re- attach it to the email to return it

You'll need a PDF converter.
I use this one pdf2doc.com/

It will convert the document to a word processing document. If you don't have word processing software then download something like OpenOffice. It's free.

Once you have all the necessary software in place just follow the instructions on the PDF converter.