I have only seen PDMAs as porter described.
I have seen the MMS? Medical Marketing Safety? ones, I think they're called.... where you go to drugstores, pharmacies, and medical offices, take pamphlets, read them, and scan and upload them. You answer a few questions like "What is the drug/treatment found? What are the FDA approved indications?" Does this informational brochure indicate anything other than the FDA approved indications?" If so, you write that section out, word for word, and upload an additional scan, a close-up of that one.
They don't pay much, at only $12-$15 per pop, but it adds up if you are doing a medical office complex, where there can be 15-45 offices, all with waiting rooms. Unfortunately, some are total busts, as you are only allowed to evaluate the brochures available to the public (in the waiting room) not any which they keep behind their desks and hand out to patients. Some offices have no pamphlets in the waiting area, so... total busts.
The other drawback is that you are paid per location, not per pamphlet. If you get offices which only have one or two pamphlets in the waiting areas, it's quick and painless. The ones which have a ton... totally suck. You have to scan and upload all of them.
The major plus for me, is that you are normally allowed to choose your own locations, if they've not been evaluated recently.
I only get an email to do them about once a year, I think sometimes 18 months? But every time, I sign up for three local medical complexes. There is a lot of prepwork involved because if choosing your own locations, you have to look up and provide the office name, doctors' names, and the address, including Suite #s.
------------------------------------------------
Plan the work. Work the plan.