Legally, no. Practically, if you do, ensure it is the "Redline version (RLV)" which shows changes. Most free copies are scanned hard copies that are not text-searchable and often missing Annexes (which contain critical calibration formulas).
IEC 62478 is crucial for several reasons:
While the traditional IEC 60270 standard focuses on galvanic/electrical PD measurement (quantified in pico-Coulombs), it requires a direct connection to the high-voltage circuit via coupling capacitors. This requirement limits its use for continuous, online monitoring.