It is very common, in correspondence or orally, to need to refer to other documents, be they statutes, case-law or evidence. You will very rarely write anything that does not talk about other documents.

It is well worth thinking about how you do this. Writing something like “Such and such was laid out in the company’s policy” can cause problems. Often the policy will be long, and there may even be more than one. Your reader will have to search through pages of documents to find what you are talking about. Even a short submission of a couple of pages, will probably refer to a dozen or so other documents at least, so these problems add up quickly.