In my understanding, a Document Controller is responsible for documents control. If we check the requirements of ISO 9001:2015 we can recognize that a good document control means things like:
No unapproved relevant documents in the QMS;
No obsolete documents in use;
People that need a particular document have access to the last approved version
Records are well protected and easily retrievable when needed
How do an organization check these requirements? Systematically, through internal and external audits. Or through random events communicated by people working in the QMS.
So, indicators to measure a Document Controller performance can be:
Number of document control related audit nonconformities (internal and external)
Number of obsolete documents in use (for example, in some sectors like pharma, some documents are published with a planned obsolesced date to promote mandatory review, and organizations have planned checking activities
And remember, I would use the term KPI with care. An organization where everything is “key” nothing is “key”. I know very few organizations where top management would call document control indicators as “key”.
Below you can find more information about document control: