Legal Question in Civil Litigation in California

If you want to verify that the other person signed the document, attach it to a request for admission. If you want to verify certain "facts" contained in the document, just ask interrogatories about the "facts." Or, you can do requests for admissions concerning the facts and also propound form interrogatory 17.1 which requires an explanation of a denial.

Sometimes it's more efficient to take the other person's deposition and ask your questions.

You are correct, but as Mr. Cohen gives examples of, it is easy to work around. You can also ask questions about documents that have previously been produced or that are known to exist and can reasonably be described in the question - no need to attach them.

You cannot attach exhibits to special interrogatories. That is what is meant when it is said that each interrogatory must be "full and complete in and of itself." The other attorneys have given you examples of other discovery devices to use to get what you want.