InstallAware

The original install WinPcap_4_0_1.exe (4.0) is created by NSIS, sized 549k.

Use decompress then the created installer size is more than 680k.

Is it normal?

Yes, sometimes it might happen , because it's converted to a MSI compatible format (NSIS it's not, it is use its own format) and some overhead from the IA bootstrapper makes it a liiittle bigger.