ISO-9001 deals with how a company is managed. In layman's terms its somewhat like this:
In a normal company the management does not know how things happen. Its handled by bob, and bob may do it differently each and every time. Now it might be that a client wants the end result to be as predictably within the agreed norms (quality). This then means that the business needs to know what bob does, how he does it and that he always does the required items in the same way. To do this each company documents their own processes and gets these processes reviewed by an external agent periodically to ensure they actually follow the process they described.
To hold the ISO certification the company must follow the process they describe. That is what ISO-9001 says, "we know what we are doing, and we intend to continue doing so". The certification does not say how, its the company's internal documentation that says how. For pharma companies this is not optional either they do it or stop being pharma companies.
For you this means that there is some requirement on how the job is checked in and how versions and revisions are handled. It may also include info on how you should test and what requirements you must meet (need to be good for visual impaired for example). It can also include provisions on what kind of contract you must have with the company to be able to do so.
Clarification: Each company has their own Quality manual, so you need to get their quality manual or requirements from them.