Standards evolve. The official PDF ensures you are using the exact version required by your Notified Body or customer contract.
The procedure involves measuring the signal level transmitted through the shield over a frequency range (typically 10 kHz to 40 GHz) and calculating the difference from a reference calibration. en 50147-1 pdf
While you might be tempted to find a free scanned copy of the , there are significant reasons to use the official version: Standards evolve