If you have an original copy of a document or photograph, do not do anything do that paper or photograph that cannot be undone. Particularly do not do anything that could potentially cause damage. If you are going to “clean” an item, make certain that the way in which you are cleaning it does no harm. Find this out from an expert who actually knows what they are talking about and is someone with a reputation you can verify. This does not include random people online who you had never heard of before you read their post.
Putting an item in a frame or an envelope (usually) is one thing. Taping it in a book is another. Taking a digital picture of an item is usually harmless–especially if no flash is used. Running it through an auto-feed scanner may not be harmless.
If you want to somehow modify the item in some sort of artsy way, use a reproduction for that modification.