To make the form ready for input, you need to use SET_USAGERIGHTS( ) to assign the usage rights. If you do not make any additional settings here, all usage rights are activated for the interactive form by default.
SET_TEMPLATE( template, FILLABLE = ABAP_TRUE ).
SET_DATA( data ).
SET_USAGERIGHTS( ).
SET_TASK_RENDERPDF( ).
EXECUTE( ).
GET_PDF( ).