The below abap code demonstrates how to implement a file selection popup onto your ABAP report selection screen field.
*Selecting a File, plus inserting default file extension parameters: p_file like rlgrap-filename default 'c:\hesa.txt' LOWER CASE. ************************************************************************ *AT SELECTION-SCREEN ON VALUE-REQUEST FOR P_FILE. AT SELECTION-SCREEN ON VALUE-REQUEST FOR P_file. CALL FUNCTION 'WS_FILENAME_GET' EXPORTING def_filename = p_file mask = ',*.xls.' mode = 'O' title = 'Upload File'(078) IMPORTING filename = p_file EXCEPTIONS inv_winsys = 1 no_batch = 2 selection_cancel = 3 selection_error = 4 OTHERS = 5.