You should be able to attach a document to an approval email using flow.
We are now working on the functionality to attach files to Approval requests.
I'd be very interested in this feature as well...
@Sunay - is there any update on this by chance?
We have engineers working on enabling the functionality at this very moment!
Please stay tuned - your patience and feedback is appreciated.
I am the engineer activey working on this feature. All I can say is soon™
That's good to hear, @TCambs - thanks for letting us know!