You can offer a user the ability to locate a file on their local computer and submit it to you via a web form, like..
<form id="myForm" enctype="multipart/form-data" action="/formHandler.php" method="post" >
<label for="fileUpload">File to Upload:</label>
<input name="fileUpload" id="fileUpload" type="file" /><br />
<input name="submit" id="submit" type="submit" value="Upload Now"></form>
Then you can process it on your side with PHP, or whatever you have on the server end. Since PHP is one of your tags, you can learn more on how to access, and work with, on the server end from the PHP reference site:
http://www.php.net/manual/en/features.file-upload.post-method.php
I hope I understood your question correctly..