File size increases 100 times after digitally signing

Hi,

I am using Acrobad 10.1.1. on a Windows 7 machine. When I digitally sing the document, the size increases from 30kb to 3Mb. In the past, with Acrobad 9, the size increased to only 100kb.

What could be the reason for this and how could I reduce the size to 100kb again?