I mean, each of them I safely downloaded and read, but if you want to be extra safe, you can disable JavaScript in most pdf viewers, it seems like that might be a good idea in general. (Some PDFs (but not these) have included some simple JavaScript to allow one to comment or edit PDFs (for example, filling in your name and signing a contract) it's in these features that malware can be hidden)

I just like downloading and reading PDFs when I'm not in range of internet.