How Can I Embed a Payload in a Working Pdf File ,So That, the One Who Opens It Wont Know Its a Malacious Pdf?

I was thinking if i could download an ebook and then embed a payload to it and then send it to my friend so that when he opens the book the file opens normally with its contents and at the same time the code gets executed. In this way he could enjoy reading the book and i would enjoy with the meterpreter :)