It sounds like using our Sign-up Forms to collect those details and then sending out a Welcome email with a link to download a document is what you're looking for!
We have a couple of different Sign-up Form options that may fit your needs. They're call the InLine Form and the Pop-Up Form. As soon as you have those set up, you can set up that Welcome email.
If this isn't what you're looking for or you have additional questions, please let us know!