As for a free PDF download of IEC 61537, I couldn't find a publicly available link. The IEC website (iec.ch) provides a purchase option for the standard, but it doesn't offer a free download. You can also check other websites, such as:
or your national standards body (like ANSI in the US, BSI in the UK, or DIN in Germany). Corporate Subscriptions : Many engineering firms subscribe to services like IHS Markit ASTM Compass Iec 61537 Pdf Free Download