I would like to upload the pdf of a paper on my new google site. Specifically, I want that people can click on, say, "paper_title" and can visualize the pdf and, if they want, download it.
I would like if possible a step-by-step explanation. Thanks!
This is fairly straightforwards:
Firstly, store the PDF files on Google Drive and, set the link sharing as appropriate (e.g. anyone with link can view) so even anonymous internet users can see the file.
To make the PDF available via Google Sites you can either:
From Drive, copy the link to the file, and in new Sites insert a text box and include the hyperlink to the PDF file in the text box.
in new Sites Insert (From Drive) and select the PDF file from the Google Drive; gives the same result as above, but with a re-sizable thumbnail picture of the PDF file instead of a link.
Exactly what happens after they click on the link is going to depend upon what browser the user is using, and what (if any) PDF viewer plugin is installed. Chrome, pretty much does what you want: it opens the PDF file in a viewer, from where you can download it.
Even if you don't store the PDF on Google Drive, what is described above should still work, as long as you have a hyperlink to the PDF file.