How to Run Homebrew's Caskroom/cask/pdfinfo?
Homebrew cask installs pdfinfo in

/opt/homebrew-cask/Caskroom/pdfinfo/latest/PDFInfo.app


And then creates a symbolic link to this locations in:

~/Applications


You can run installed pdfinfo with:

open -a pdfinfo


or

open -a /opt/homebrew-cask/Caskroom/pdfinfo/latest/PDFInfo.app


or

open -a ~/Applications/PDFInfo.app


Simply you can open app with double click on ~/Applications/PDFInfo.app icon.