This is a temporary package, which is used during a test phase
to load the new PDF management code of LaTeX. The new PDF
management code offers backend-independent interfaces to
central PDF dictionaries, tools to create annotations, form
Xobjects, to embed files, and to handle PDF standards. The code
is provided, during a testphase, as an independent package to
allow users and package authors to safely test the code. At a
later stage it will be integrated into the LaTeX kernel (or in
parts into permanent support packages), and the current
testphase bundle will be removed.

Homepage:
https://ctan.org/pkg/pdfmanagement-testphase
