Found this on the web. Worth a try.
"If you want to open PKPASS files on Windows PC, then it’s actually simpler than doing it in a phone.
As PKPASS is a compressed archive just like .zip and .rar, so you can rename it with .zip or.rar extension, then you will get access to the contained information by extracting the file."
Alternatively, there are apps on android and IOS that claim to open this file type.