How to restrict attaching documents from other document classes that user is not enabled to create document revisions?

Hi @Nethmini Kosvinna , As far as I know, I assume we cannot restrict attaching option to specific set of document classes for a user. But, if you set a document class as a restricted access (either from Document Class Management> Document Default values> RESTRICTED_ACCESS value 'Y'  or when creating doc revisions, ticking the checkbox), user should have at least view access to the document to see its general information. So, by setting this, when attaching documents to objects, in the document revisions list, users who do not have at least view access will not see those revisions with restricted access checkbox checked. To make sure the user does not get view access to documents created on a specific doc class, you can further set up this on Document Basic>Access template tab, enter the user ID and clear all three levels of access.

Hope this will be helpful.