There is currently no means to limit the number of times a document is uploaded, only a means to limit the maximum size for Attachments - the default is 25MB. We understand the need for this sort of feature and have created an Idea on our Community page to this effect. Please navigate to https://community.blackbaud.com and log in or create an account. Once logged in, you may navigate to the Idea page below in order to comment and vote on the Idea:
Remember, the more votes an Idea receives, the more traction it will build with our Product Managers, so please encourage your colleagues to vote on the Idea as well!