Re: Saving an pdf file
That's because that link is a fully automated download link. The end user needs do nothing more than click on it to have the PDF file that is ahead of the final '/download' part of that link download to their machine simply by activating it.
I supply this sort of link all the time, e.g., . If you look at the actual URL for this it contains the word "download" in the URL and that's generally (almost universally, actually) an indication that activating said link will trigger a direct download. In some cases you'll get a Save As dialog if your web browser is set to ask you where you want to put any file you download and in others it will go directly to Downloads or whatever folder you've specified as your download location if set to do that.
The person who set up the sourceforge page, https://sourceforge.net/projects/linuxcommand/, which is the root page on which the download link you gave and several others are found, really did not know how to create a well-designed page where links that trigger downloads would have used click through text to indicate that's what would happen. The link you provided, if following good practice, would be listed on the page as, Download TLCL-17.10.pdf, or something very similar, just like I did in the middle of this sentence.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore