31.(1) When any instrument, whether executed or not and whether previously stamped or not, is brought to the Collector, and the person bringing it applies to have the opinion of that officer as to the duty (if any) with which it is chargeable, and pays a fee of such amount (not exceeding five Taka and not less than fifty poisha as the Collector may in each case direct, the Collector shall determine the duty (if any) with which, in his judgment, the instrument is chargeable. (2) For this purpose the Collector may require to be furnished with an abstract of the instrument, and also with such affidavit or other evidence as he may deem necessary to prove that all the facts and circumstances affecting the chargeability of the instrument with duty, or the amount of the duty with which it is chargeable, are fully and truly set forth therein, and may refuse to proceed upon any such an application until such abstract and evidence have been furnished accordingly: Provided that-(a) no evidence furnished in pursuance of this section shall be used against any person in any civil proceeding, except in an inquiry as to the duty with which the instrument to which it relates is chargeable; and (b) every person by whom any such evidence is furnished shall, on payment of the full duty with which the instrument to which it relates is chargeable, be relieved from any penalty which he may have incurred under this Act by reason of the omission to state truly in such instrument any of the facts or circumstances aforesaid.