How to add a passport to my iPad Pro?

To my knowledge, no passport agency has yet permitted Passports used for international travel to be added to electronic devices.

Border Agencies require presentation of the original document. The majority of modern passports now incorporate NFC-readable encrypted security information about the document holder - this information only being accessible to the electronic reader when unlocked by an optical scan of the main photo page of the passport.

The Wallet App is unique to iPhone due to hardware…

The iPhone Wallet uses NFC to wirelessly communicate with physical Point of Sale (PoS) terminals - NFC being the mechanism used by ApplePay (and Google’s Android equivalent) to securely exchange registered Credit Card details and authorise a payment.

The Apple Wallet App has dependency upon NFC hardware which is absent from all models of iPad. Consequently, the Wallet App is not available for iPad. Whilst perhaps a moot point, consider the practicalities of attempting to bring a specific area of an iPad (which may be sizeable) within close range of a PoS terminal!

Whilst iPad does not have a Wallet App per-se, iPad does have Wallet in iPad settings. Here you can register Credit Cards for ApplePay - but this is not intended for NFC. Instead, iPad is able to participate in remote e-commerce payments - such as a website.

I hope this explanation brings useful clarity as to the capabilities of both iPad and iPhone in context of ApplePay and Wallet.