I don’t know of an existing solution to this off the top of my head. To get the map fragment, it is possible to use the tiles from the OSM server. If your application is likely to generate many requests, this could be blocked in the future however. The marker would need to be added with image processing software, or possibly to the PDF as a layer (I don’t know about PDF).
a very good looking open source web service that generates PDF maps ist http://www.maposmatic.org … look at their sources and the map results … is that in the direction that you need?