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I use the latest version of doPDF. My OS is Windows XP Professional (German). The initial height was 55.1 inches. I just found out the following: doPDF can handle the conversion of the inch values of both width and height if and only if the resulting mm value is smaller than 1000, that is, 39.3 inches is OK, 39.4 inches is not. I hope that helps.
Thanks for the details, but this must be something regionally specific. dopdf can accept width/heights of up to 3276mm (around 128 inches). I've also tested this and it's no problem adding a value more than 40 inches, but then again on an XP in English not German. Can you do a test and go to Control Panel-Regional and Language options and try to set United States instead of Germany in there? After that see if this bug reproduces, and you can turn your preferences back to how they were after the test.