Thank you for your post.
I am able to replicate the problem. Wondering if this was a FileMaker Go or iOS 6 issue, I tried this under iOS 5.1.1 on an iPad 1, and I also received the same results. The file under 12.0v4 was approximately 880 KB, while under 12.0v6 (Latest release) is 10MB.
I have forwarded your post along with my findings to our Development and Testing departments for review. I will keep you posted as information becomes available to me.
With iOS 6, there is now an extremly useful feature: when you use the Camera to add a picture on a Container, you can choose the resolution (Small, Medium, Large or Full).
20 pictures in Full : PDF of 20MB
20 pictures in Medium (the Small resolution is really too low) : PDF of 0.8 MB
That's a perfect temporary fix.
And there is something even better: the size of the database will be reduced a lot.