want to convert a .pdb file to a file compatible with my kindle like a .doc or .txt?

i just bought a kindle and have some books on my computer that I bought from barnes and nobles however those books are in a .pdb type file to be used on devices such as an ipod and are not compatible with my kindle. I was wondering if there is a way to convert them to a file that will work on my kindle like a .doc or a .txt? i dont know much about doing this sort of stuff so i need it to be simple! thanks
I tried the thing karl b recommended but after it converts it to a new file the text is all garbled and symbols! ugh im so lost!