EMS_UDF_PDF is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "User-Defined Fields - Form Context" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_EMS_UDF_PDF TYPE EMS_UDF_PDF.
The EMS_UDF_PDF table consists of various fields, each holding specific information or linking keys about User-Defined Fields - Form Context data available in SAP. These include KV_TECHNICAL_ID (Key-Value: Technical ID), DOM_TYPE_KEY (Key for Domain Type), ACTUAL_VALUE (Key-Value: Value), TARGET_VALUE (Key-Value: Value)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .