1) First unzip the package:
gunzip netvault-R2016FEB26-v11.0.0.52-Client-SolarisIntel.tar.gz
This leaves you with:
netvault-R2016FEB26-v11.0.0.52-Client-SolarisIntel.tar
2) Now extract the tar archive with:
tar -xvf netvault-R2016FEB26-v11.0.0.52-Client-SolarisIntel.tar
You may achieve both steps in one command:
gzip -cd netvault-R2016FEB26-v11.0.0.52-Client-SolarisIntel.tar.gz | tar -xvf -
This leaves you with a netvault/ folder.
3) Now that the netvault/ folder is available:
cd netvault
pkgadd -d .
If you wanted to run the installer from the parent directory without javing to 'cd netvault', then run:
pkgadd -d netvault
and the installer should start.