In order to get a list of the available paper trays for a printer you need to use the GetPrinterBins function in Foxit Quick PDF Library. This function will return a list of the available paper trays and associated values. You can then use the returned value with the SetupCustomPrinter function to print your documents to the relevant paper tray.
Here’s some sample code in C# to show you how to use the relevant functions.
string printerName = DPL.GetDefaultPrinterName(); string bins = DPL.GetPrinterBins(printerName);