Hi James,
the Motorola EMDK contains support and sample to develop application that interact with the FX7400. Latest version for .NET is available here:
http://support.symbol.com/support/search.do?cmd=displayKC&docType=k…

Installing this latest EMDK for .NET, you will find libraries, docs and some sample code:

CS_RFID3_Host_Sample1 Shows how to use Symbol.RFID3 assembly to perform basic inventory and single tag access operations (read/write/lock/kill). This sample is designed to run in a host, such as a PC, to remotely control RFID-enabled devices. Host (PC) based application : FX7400, XR series (LLRP enabled)

CS_RFID3_Host_Sample2
Shows how to use Symbol.RFID3 assembly to perform advanced inventory and tag access operations (read/write/lock/kill) on single and multiple tags based on filters (pre-filters, post-filters and access-filters), reader capabilities and configuration and reader management functions. This sample is designed to run in a host, such as a PC, to remotely control RFID-enabled devices. Host (PC) based application : FX7400, XR series (LLRP enabled)

CS_RFID3Sample3
Shows how to use Symbol.RFID3 assembly to perform basic inventory and single tag access operations (read/write/lock/kill). This console sample is designed to run on the device. FX7400, XR series (LLRP enabled)

CS_RFID3Sample4Shows how to use Symbol.RFID3 assembly to perform advanced inventory and tag access operations (read/write/lock/kill) on single and multiple tags based on filters (pre-filters, post-filters and access-filters), reader capabilities and configuration functions. This console sample is designed to run on the device.. FX7400, XR series (LLRP enabled)

Best regards
Pietro