[robertlagrant]

Why would you need to pay $40 for a PDF of a paper published almost a hundred years ago? What makes the paper not public domain?

[seanhunter]

You don't. It is public domain. You pay that if you want to get it from them. This is the same as I can get a free pdf of "Linear algebra done right" from Sheldon Axler's website but if I want to get it from Springer I pay $50 or whatever it is.

[robertlagrant]

That is a very confusing state of affairs!

[ChrisMarshallNY]

Repackaging and selling free data is a very old business model.

In many cases, it's value-added, because the bundler may also do some curation and interpretation.

Not sure that's what's happening, here, though...

[esterna]

You can also buy licenses to use AV1, a royalty-free codec.