Metadata missing DOI

[abhinavdayal]

When we parse metadata of a pdf it ignores certain important keys. See screenshot comparing metadata extracted using PyMuPdf vs that from PyPdf2

[JorjMcKie]

You are right: The Document.metadata property only returns key-values that are part of the official PDF specification.
Another motivation is that PyMuPDF not only supports PDF but half a dozen more document types, which also have their own metadata configurations.
But for PDFs, there are easy ways to get and set arbitrary other, "private" key-value pairs - see here in the documentation.