You can set the link to expire and limit the number of views. In production the recipient confirms access with a one-time code sent by email before the document opens.
Sessions and time per page count only after the recipient agrees, on the PDF page, that your company may see how long they read its documents. Until they answer, and after a refusal, HawkOpen measures nothing, shows you no session and keeps no IP address.
PDF links per month: Free 5, Pro 10, Business without a monthly limit.
A session or page time shows that the document was open in a visible, active browser tab. It is not proof that someone read it.