Contribute plugin and file types

I am not sure about this. When I use the contribute plugin, how can someone contribute a pdf document or even a doc file? Do I have to somehow add that option to go along with story, image, audio movie?

No, they can upload a doc or a PDF to any of the types offered in the contribution plugin. It is possible for someone to choose an image and upload a PDF or Doc that contains images. The only challenge is that no thumbnail will automatically be created for the doc, for example, even though most images have thumbnails. But, contributors will not be restricted by file type.