Microsoft is obligated to host the PIFF standard

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Microsoft published a Protected Interoperable File Format (PIFF) specification in 2010. It defined another usage of multiple encryption and DRM systems in a single file container. PIFF brand was registered by the MP4 registration authority in 2010.

https://github.com/MicrosoftDocs/iis-docs/files/13983117/Protected.Interoperable.File.Format.PIFF.1.1.pdf

PIFF is still used by popular websites today, such as https://hulu.com. as such, I feel Microsoft has a duty to host this PDF on one of their official domains. otherwise, it forces users who wish to implement the spec to search random websites trying to find it.