responding on e mail attachments

I was sent a letter as an attachment. i was asked to read it and make any changes on it and send it back, how do i do that. i saved the attachment on my desktop.

thanks..

I have never done that on a mac, but I used to do it on ms... I would either copy it into notepad or word. Using word I would highlight the original in one colour and then use another colour to make changes (or use the make changes feature in word - if I remember correctly, I haven't done that or opened either in ages). With mac you can use text edit and do the same as I do in word as it's a very powerful built in program.