the mission is about creating a website similar to [login to view URL] (provided here as example and explanation only)
Visitor can drag n drop pdf file and download resized smaller pdf, without need of login etc.
30 freelancers are bidding on average $311 for this job
You could utilize iText lib which can be installed on your web for free. Then the page you will design will have an access this library and pass the file as the argument. The backend scripting would be zPHP