Hi Sarda,
Hope following will resolve ur doubts:
1) Din 4 is not applicable for foreign citizen because such persons do not hafve pan cards. But if such persons hold indian pan card than DIN4 will become mandatory.
2) In case of existing din if the din holders belive that he has already provided is pan at the time of applying the din than he must not applies again. However saying that it shoud also be noted that for Filing DIN4 there is no roc filing fees and hence you should file the din 4.
3) for safety purpose you are advice to download DIN 4 form and insert pan no. in the form and click on the auto fill button. if the name mentioned on the pan card matches with the DIN name then it is the hint for you not to apply for din4 as the database available with the MCA matches with the Income tax department.
Regards
Vaibahv Sisodiya
8080671477