AppxSignature.p7x

PKCS #7 signature file Reference

A .p7x file contains a digital signature in the PKCS #7 format. Windows app packages in the APPX and MSIX formats keep their signature as AppxSignature.p7x. The signature covers the package content through a block map of file hashes. Windows validates the signature before it installs the package. The file is binary.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.