From the Count Pages first Post - end of para #4
. . . the configuration you can choose to use the page count used by the calibre e-book viewer, or you can use the Aobe algorithm used by their ADE software and some devices like a Nook. However if the format being counted is a PDF, then as of v1.4.2 there is now a special optimisation to read the actual page count rather than estimating it using any of the above algorithms.
. . .
And from the Count Pages Version Log
Version 1.4.2 - 31 May 2012
Minimum version set to calibre 0.8.54
Optimisation for counting pages for PDFs to read the page count from the PDF info rather than estimating it
Zo, i just did a small test with 7 PDFs of various provenance - here are the results
The numbers in the Titles are from File Explorer/XChange Document Properties. The Have Read indicates if Count pages got the right answer. Books 2 & 4 are rubbish documents that I created with a online Form layout tool, I can't explain the first one (A 4 D) - if anyone wants that PDF to take a look at what's going on let me know.
The bottom line is that Count Pages does not handle PDFs by converting it to a reflowable format, it gets the page count from the same place as File Explorer - most of the time Ψ³
BR