IDoc is the abbreviation for "Intermediate Document", a widley used standard to exchange business data between systems, mostly SAP Software based systems. With an implementation of the classic Business Add-in (BAdI) IDOC_DATA_MAPPER, you can change values in inbound and outbound IDocs via ABAP programming.
How to do that is the topic of this repository. It contains a small, not syntax checked example as reminder. Please check also this SAP Community Blog for more detailed tips, hints and tricks.