It doesn't mention Writeln anywhere. In section 13 (page 39) "Input and Output" it only mentions read and write for text input/output and at the end of it mentions that the end of each line must be indicated with the EOL characer. A few pages later (page 44) there is a table of standard identifiers and there is no mention of writeln either (but there is of write).
This looks like the manual for the Pascal 6000 compiler they had at ETH Zurich which extended the language that Wirth described. In fact in the preface it mentions that the standard is the "The Programming Language Pascal (Revised Report)" which in footnotes mentions is the 1973 version - ie. the document i linked above.
Confusingly enough though it does describe readln and writeln in an attached revised report (mentioning that the reason for their addition is that they can't rely on an EOL character being available) but this is not the text they cite as the standard Pascal nor the latest version of the report available from ETH themselves (which is basically a different scan of the same text i linked above): https://www.research-collection.ethz.ch/handle/20.500.11850/...
My guess is that they added these at some point later but didn't make a newer version of the standalone report (which is what i've seen in other places, e.g. http://pascal-central.com/standards.html refer as Wirth's last standard). I guess in practice it was simpler to have a single book act both as a tutorial and a reference, though i always though the 1973 report to be the last "standard" and didn't paid much attention to the other stuff released later.
Quoting the "Preface to the Revised Report" in my link: "...the language defined in THIS Revised Report is called STANDARD PASCAL." Two paragraphs later: "... the new procedures READLN, WRITELN, and EOLN have been included in the set of standard procedures..." Sorry that ETH has outdated stuff, but this is an accurate image of the actual, physical book authored by Wirth, as published and sold by Springer-Verlag, in which he says it describes STANDARD PASCAL. I have it in my possession if you don't believe the scans that are on the internet.
Uh yes, i believe you, i just mentioned that it is confusing that the first part of the manual refers to the 1973 report as the standard Pascal and then the report in the second part is not the exact same text and that the last revision available from ETH is not the latest one (most likely because there wasn't a standalone version made) doesn't help.
http://pascal-central.com/docs/pascal1973.pdf
It doesn't mention Writeln anywhere. In section 13 (page 39) "Input and Output" it only mentions read and write for text input/output and at the end of it mentions that the end of each line must be indicated with the EOL characer. A few pages later (page 44) there is a table of standard identifiers and there is no mention of writeln either (but there is of write).