Need help with Plugin or theme for selling services

Hi there,
I am new to wordpress and I am trying to set a new website where users can send me a file to work on (the file is to me to do data entry on it) and then when I am done working on it I could attached via the wordpress so they could download the worked file. I need two that they can pay before or after they upload or download the file with pay pal or other services and they can see what files they have upload it. Does anyone have an idea how I can achieve this or what plugings can I use or point me in the right direction?
Thank you.