It was written in Bliss so not so hard if you understand BCPL or C. Also I was 17 and had a lot of time on my hands...

I think (s)he wonders how you read that.

My guess would be that you did using the microfiche reader at your university or at a library. Before digitization, such devices were fairly common wherever people had a lot of text to archive.

(Aside: https://en.wikipedia.org/wiki/Microform even has a photo of a “DuKane brand microfiche reader with source code printed on the films.”. I couldn’t read enough of the text on the envelope to decide whether that is true from the photograph

Oh yeah. I worked at a defense contractor so we had facilities to read and print out Microfiche.

30 or so years later I bought a huge stack of DEC microfiche on eBay so I could still do it if I wanted. I don't have equipment to read it though.