Every layout comes from the same drawing code, so the preview, the PDF, the printout and the image are the same calendar. Text uses Helvetica (Arial on screen, which has the same letter widths), so what fits in the preview fits on paper.
Dates follow the Gregorian calendar. Week numbers follow ISO 8601 (weeks start on Monday; week 1 contains the year’s first Thursday). Moon phases are calculated with Jean Meeus’s method for the time zone set on your device.
Sources
Holiday dates generated with python-holidays and checked against official government lists
ISO 8601-1:2019 week numbering
Jean Meeus, Astronomical Algorithms, 2nd edition, chapter 49 (moon phases)