[marcoc]

How can one create a professional looking pdf like the QOAF specification one?

[GraemeMeyer]

Two-column layout in Microsoft Word, large header, smaller footer, with appropriate font choices would get you basically all the way there.

[jfk13]

HTML+CSS, converted to PDF via the Save As PDF feature in Firefox. (Or the same could be done with other browsers, but this one apparently comes from FF.)

[crumpled]

I looked at the PDF, and can confidently say I could typeset that in a word processor, using a stylesheet to sustain it.

That's not what they did, apparently.

The document properties call out https://cairographics.org

[kenferry]

Cairo’s a couple layers down from what you’re talking about. It’s the actual glyph rendering.