How to attach a document (resume) when replying to a job posting?

I am on Craigslist trying to respond to a job posting by clicking the Reply button & my email (gmail) opens a new message window properly but I can't attach my resume to the email which is what I need to do in order to respond to the posting. In the past, I have done it this way, typed the email message, copied & pasted the reply to address in the body (for later), then sent it to myself instead & then had to go back into my email from a desktop to attach the document, cut & paste the reply to address back into the To: field & delete anything in the body of the email showing I was now forwarding it to the company instead of responding straight from the posting.

This is too much of a headache & I am hoping that I just don't know the proper way to add a document attachment (.pdf, pages, or word) & that its not that Apple just hasn't figured this into even the iPad 3.... Please help.. Job hunting ***** by itself but having to do all this to attach my resume really *****!!