Can you add "attachment" function in zoho books?

Can you add "attachment" function in zoho books?

1) If we collect cash from client, so attachment function is useless for us; but sometimes our client online transfer money to me, or using ATM machine transfer, or using credit card transfer payment, in such case we must receive his BANK SLIP PROVE before we record payment. So, the attachment function play a big role!! It is time-wasting to type the bank slip reference number one-by-one as all the bank-slip number are very long. Due to not waste time on typing, now we store bank slip in google drive, and every time we need to switch between two place to check the payment details and this affect our working productivity.

2) Besides from record payment part, other part in zoho books which should have attachment function also...
• invoice:  sketched pattern or other related documents can attach in so that no need do long explanation in product description!
• invoice record payment:  bank-slip! bank prove!
• expense and bill: can store vendor's invoice or statement


!
• expense and bill payment made: can store our company bank-slip to suppliers! 
• contact: can store vendor monthly statement!

3) Can you add this up asap? This function is not so hard to deploy right? Hope could get your good news!