That's interesting, I absolutely hate PDF. Lack of metadata for collecting, format is difficult to support, doesn't layout well on mobile, and very limited customization (like dark mode, changing text size, etc).
Only benefit is browsers have built-in support for the format.
One thing I like about PDF is the annotations (notes & highlights) are embedded in the PDF itself. That is not the case for EPUB files, each EPUB reader stores annotations in its own proprietary format.
Very true, I just rolled out annotations for Kavita (a self-hosted book/comic server) and epub doesn't have the ability to store it in the file (although Kavita has a no-modification policy).
Although for cases like Kavita, storing in the file would be problematic if multiple users want their own annotations without concerns of data leaking.
PDFs have pretty excellent support for metadata. If the collection software doesn't support at least Dublin Core, that may be kind of their own fault...
I haven't seen this in the real world or the tooling to back it up. Currently, Calibre is the only software that writes metadata that pulls from online sources.
I'm sure Adobe Acrobat also supports, but that's not used in the scene.
Feels like a very big gap in the OSS world then. The PDF spec supports multiple standards for metadata, Acrobat has workflows for all of them, and Adobe sells into a bunch of verticals (such as public libraries) that rely on this functionality heavily.
Only benefit is browsers have built-in support for the format.