https://answers.sap.com/questions/7106559/special-character-%27%27-in-smartform.html  

DATA:LV_TDTAB_C132 TYPE TDTAB_C132.
CALL FUNCTION 'CONVERT_ITF_TO_ASCII'
EXPORTING
CODEPAGE = '0000'
FORMATWIDTH = 128
LANGUAGE = SY-LANGU
TABLETYPE = 'ASC'
TAB_SUBSTITUTE = ' '
LF_SUBSTITUTE = ' '
REPLACE_SYMBOLS = 'X'
REPLACE_SAPCHARS = 'X'
IMPORTING
C_DATATAB = LV_TDTAB_C132
TABLES
itf_lines = lt_lines
EXCEPTIONS
INVALID_TABLETYPE = 1
OTHERS = 2
.