thank you for reply.

the print function with second parameter TRUE,
shows system printer dialog, but the printer property paper size is not bring from windows printer setting to PB.

i think it is a print function bug/issue.
i do below test, in windows 10 , two printer setting:

printer1 - "Microsoft Print to PDF" (use default A4 paper size) [set as default printer]
printer2 - "Microsoft XPS Document Writer" (assign custom 7x5cm paper size)

application run dw_1.print(true,true)
show print dialog, then choose printer2 and click "property", you can see paper size is not correct.
(print out is also not correct paper size)

yes,you can re-assign paper size in property setting, and print out correct,
but when you close window and reopen window, and run .pring(true,true),
the paper size is back to privous.

In fact, application user wouldn't re-assign paper size every time when print.
I also test it in user site, print out to real printer, also still got paper size issue.

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maybe i must code all datawindow print.properties as you say,
i think it is not make sense.

finally, i use below script for woraround, but can't set page range.
PrintSetup()
dw_1.Print(true, false)   //do not show system dialog