before you go any further, take a look at container fields and see if you can get them to work for you. A container field can store either a physical copy of a file or a reference to where it is stored. This can be a method for handling your "attachments".
You'll also need to think about how to set up your tables for this. I recomend you set up a documents table where you have one record for each such document. Then add additional fields to describe this document that you will use to search for it by performing a find.
I updated my post with a screen shot.
What I said earlier still applies.
Since you have a field for the Filepath, you also have the option of using Open URL with the contents of this field to open the document, but you mentioned enabling users to download the file and that is best done from a container field as you can then use Export Field Contents to copy the file to the user's computer.