Went to check the manual, and found it points to a URL on the developer's website that no longer exists.

Why not just include a PDF of it in the game directory, and have the link in the Steam client open that?

EDIT: Oh, wait. There IS a PDF of it in the game's directory! Now why doesn't the link in the Steam client point to it?

EDIT 2: And annoyingly, the resolution of the included PDF's images is too low to read the ad for the Protologic computer, which is a major reason why I was opening the manual in the first place: to read the in-universe stuff included in it.

EDIT 3: Huh. The in-universe ad is the only page that's unreadable due to the resolution. The rest of the in-universe text seems to be vector-based and scales up with the zoom in the PDF reader.