You can link the filedocument(or preferably a generalization of it) to the account entity with an association. When you create the filedoc you need to set this association.Then either with entity acces or an xpath constrained on the page you can set the constrianed to: filedocument_Account = [%CurrentUser]. This way the user can only see its own documents
In addition to Maarten;
please question yourself; is the user only allowed to view its own documents (1) or is the user allowed to see all documents, but on this particular page displays only the user own document. (2)
This will define where to add the XPath
Follow this learning path: https://gettingstarted.mendixcloud.com/link/module/35/lecture/326
This will tell you how to use Access Rules and XPath to constrain the documents so it will only show the documents of the user.