The UN uses a hierarchy in its numbering systems which corresponds to the relevant parent body/subsidiary body organizational structure. Once you understand the hierarchy levels and codes, it is much easier to find the right document.
Since the Sub-Commission is a subsidiary body to the Commission on Human Rights, which in turn is subsidiary to the Economic and Social Council, a typical Sub-Commission document will be styled as follows:
In this example
In this case, document 1 is usually reserved for the agenda of the meeting. If an "Add.1" is shown, it means an addendum has been issued with the document -- an annotated agenda if it is "...1/Add.1"
One further level of detail is required for the documents of the working groups, the Social Form, and NGOs at the Sub-Commission. A working group document will bear a number such as
where "AC.5" refers to a particular working group (in this case, the Working Group on Minorities),
A Social Forum document will bear a number such as
where "SF" refers to the Social Forum, and an NGO document will bear a number such as
It is customary when requesting a document from the current UN meeting you are attending to specify the main document number, such as "Document 1, Add.1", for the provisional agenda or "Document NGO 10" for a specific NGO document. But bear in mind that you will need to specify the full numbering sequence if you are requesting a document from a different session or a different UN body.