You don't have to attached the entire history of your bank account, I believe it was only 3 months what they are asking, see don't attach unnecessary documents, just attach what they have asked for, if you will attach additional documents such as couple of months bank statement for no reason it will only complicate your case and delay the process, if they have asked 3 months means it should be 3 months and if its for 6 months than only attach 6 months, keep in mind that thhey will consider the lowest value as proof of fund in the entire history of you bank account. PDF format is best format to provide that's what i did. Good luck!