Help with reading files

I am doing my development for our project on a Linux server, but our client uses Windows. One of the features that we have is the ability to send emails. The email feature will have a feature where the client can upload a file from their computers with a list of emails. My script would then parse out the file and send the emails. How would I access the contents of the file? We are using PHP for the development. Thanks in advance. Yasir