Backpack big enough for documents?

I would like to order a backpack on the Internet, but I'm a little unsure about the size. According to the description, the backpack is 30cm (length) x 40cm (height) x 12cm (depth) and a 13-inch laptop should fit inside.
My question now is, do A4 format documents fit in such a backpack or would it be too small again?

I would be very happy about any helpful answer!

Din a4 is about 21 by 30 cm

A4 has 21x29 so fits easily

The Läppi 13 inches is 13 x 2.54 and makes 33 cm diagonal

BUT

How high is your lap? Because 12 cm is not much.