To print to an Epson printer from the iPad you need the Epson Connect iPrint App but you also need a compatible printer eg wifi. The DX400 is not compatible and therefore you will be out of luck. See Epson iPrint compatability
How to Air Print to ANY printer from iPod,iPad or iPhoneclick here
Test out the software thru' the trial period first before you decide it's worthwhile to donate or pay for it, the handyPrint (AirPrint Activator) worked for me very well but haven't tried the PC version thou'.
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