Letter writing: Refering to enclosed items
The word enclosure can be used. It not only means something that encloses, but also something that is enclosed. Dictionary.com defines this as definitions 1 and 2 here: http://dictionary.reference.com/browse/enclosure?s=t.
It is common in business communication to say something like, "Please see enclosure 2 for a copy of my address proof," or "Please see enclosed item 2 for a copy of my address proof."
Usually, such letters have an "Encl." section right after the closing signature. For instance:
Dear Mr. Smith,
<body of your letter>
Yours truly,
Jane Doe
Encl.:
1. Copy of Master's Degree award
2. Copy of address proof
3. Copy of Social Security Number allotment letter