Can I make iTunes see a file as a podcast?

When I listen to half of a podcast or an audiobook and then come back to it later, it begins where I left off the last time, which is good. When I listen to a song, it does not do this. Recently I downloaded a bunch of podcasts that were not available on iTunes. When I put these podcasts in iTunes, they went in as regular audio files and not as podcasts. I couldn't figure out how to put them in as podcasts. Now when I listen to them, I have to start from scratch again whenever I listen to half of one and then come back. Is there any way I can change the setting for these so they will start where I left off? Or is there a way to enter audio files as podcasts or audiobooks? Thanks