Why The Toolkit DLL is much bigger than download

I download the Version 1.0.10301.0 Ajax Control Toolkit. Both of With Source code and without .I found a question.The ajax control toolkit dll file which is in the without source code package is 764KB(in "\SampleWebSite\Bin" ),but the dll file I generated from the source code is near 1.3MB. Why?

if you compiled in Debug mode, then your assembly would be larger than if you had compiled in Release mode.

oh~~~~~~~~ Right! Thanks for your help answer!