How to analyze a link to figure out the actual link

It might not be possible. The sites could feed you through a hundred redirects before you get to the file.

In addition, javascript can be used to give out links based on the URL that was given to the server.

The site could be scripted, and when it gets a certain command (the URL can pass a command), it might then return a PDF file (or some other file), without redirecting. There it's a server-side thing and depends on how the site is coded. Without actually requesting that link from the server, it's unlikely you could figure out how to get the file. And sometimes even if you knew the direct URL, you might not have permission to access the direct link. Some sites are coded so that direct links won't work.

This is pretty much the "true" URL as for those well-protected websites, you have to submit the complete URL for the server to authenticate your request. You may be directed to another URL afterwards, but it will normally be a one-time one. In other words, these file download websites will never give you a leech-able direct link.

In this particular URL, the parameters, which are protected by a digital signature, clearly list time and IP restrictions of the downloader. For a website with this level of competence, it is unlikely there will be leaked direct links.