Why are Acrobat PDF tags not shown in Windows?

Windows doesn't have native support of metadata for every filetype, because there's no general standard of embedding those in files - it always depends on the format used. Various applications can add metadata support for some file formats.

Maybe some PDF reader will install tag support for explorer, Adobe Reader XI doesn't seem to do so.

It's also possible to completely remove metadata support from Windows installation disk with software like RT Se7en Lite, but I guess you'd know if you did it.

I have the same issue and, after scratching my head for weeks looking for a solution, I wrote an Explorer extension myself.

Take a look here: http://coolsoft.altervista.org/pdfpropertyextension

It's a really lightweight Explorer extension that will bring Author, Title (and other) columns back for PDF files.

And it's free..., I wonder why Adobe & C. still don't have it ;)

This tool enables editing metadata on any file type in windows https://filemeta.codeplex.com/

After installation, you pick extension you want to enable meta data editing and bam, it's there in File Explorer

From the website

It is pretty clear that Microsoft originally intended to ship a broader capability. What this package does is wire together pieces that were built into Windows in readiness, but never joined up: it connects Explorer's ability to see and edit metadata with NTFS's support for storing property data in an annex to any file, and so allowing metadata to be added to files of any type. And because Windows Search uses the same property system hooks as Explorer, you can also search using this metadata, both in Explorer and from the Start Menu (or Search charm). That all this takes just a 17K DLL (64-bit, release build) and some registry settings tells you how close Microsoft got.