I disagree with giving up precisely because the OP is a noob and this should cause him to use his brain a little. Plus it's a kool keypad. I'm sure there is a reason he wants to use it beyond saving the $3 a 4x4 membrane keypad costs.
If you haven't done a keypad before, consider this keypad and the Matrix library:
The way most two or three key keypads work is to have a common connection and one line per key and you put +5V on the common line and when it goes high on the line that represents a key you know it has been depressed.
For larger keypads like that 12 key one above, there are 4 connections for rows and 3 for columns. The way you read it is to hold all row pins at high impedance, put row 1 high, check the 3 column pins to see if any are depressed, note which are, then put row 1 into high impedance and move on to row 2. You are scanning the rows for depressed columns.
I don't have the time or inclination to deduce the pinout of that keypad from the images posted. It looks like signals are coming from one side with the solid lines to the side with the squigglies. Each squiggly is a key. I'd number each input on that ribbon connector and correlate it to each of the passthrough pads and then put that number on the switch side and correlate each key to the two lines that it connects. If you can't do it by just looking, a continuity tester should work fine. You need to know that, you will never find the data sheet for that keypad. So figure out the pinout and then apply lessons learned in the datasheet above.