“The Errors of TeX” with hyperlinks

I was reading the appendix to "The Errors of TeX" by Knuth (errorlog.tex, written with plain TeX) and I noticed that there is a PDF file errorlog.pdf with nice hyperlinks and I was wondering how that is possible.

It looks like magic to me, since the plain TeX file apparently has nothing related to hyperlinks. I've noticed that the PDF file was generated with pdftex, so I was wondering if there is some pdftex-specific technique allowing such hyperlinks.

Does anybody know what kind of modifications are necessary (if any) in order to compile Knuth's file with pdftex and get those hyperlinks?

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