How to get the number of pages of a book without opening it through the command line about sumatrapdf HOT 1 CLOSED

That's in effect impossible as you need to run a file utility request (they must open the file to read the contents)
PDF page entries are stored in a semi-random set of numbered entries so it is possible for 2 entries from different times to only produce 1 page and also in rare cases a single page spawn another. However you will not know until the file is decrypted (if locked) or when scripts are running.

There are many command line tools like PDFinfo to report a calculated guess based on the raw count of KIDS entries, but they may not be true in 100% of all cases, all such tools will need to process a file from first to last byte. So usually its a slow task, unless they stored a set of counts from previous runs, like a database.

Here one single PDF has other PDFs nested inside it so the GhostScript count is unverified as to the total number of pages combined.

Either you run windows FindStr to look for the page count texts (if not encrypted) or a command line tool like GhostScript to show calculated number of pages that it finds by silent running through all the entries.

HOWEVER just like DocX there are files where the number of pages will change when the contents are running live in screen. This is common with Forms that self adjust especially scripted XFA ones which SumatraPDF does not run.

Above GS-estimate is based on script

@echo off 
color cF & MODE CON: COLS=40 LINES=12 & title "%~n1.pdf" number of pages 
cd /d "%~dp1"
"%~dp0\gswin32c.exe" -q -dBATCH -dPDFINFO "%~n1.pdf" 2>%temp%\output.txt
findstr  "has" %temp%\output.txt
pause
del %temp%\output.txt

from sumatrapdf.