gem wicked_pdf:
https://github.com/mileszs/wicked_pdf
source code:
https://github.com/corsego/17-wicked_pdf
blogpost Complete guide to generating PDFs with gem wicked_pdf:
https://blog.corsego.com/gem-wicked-pdf

install gem wicked pdf:
https://github.com/corsego/howto-wicked_pdf/commit/c09d4f7140c1772115f639a3fb000cfc76dc1399
send PDF as attachment:
https://github.com/corsego/howto-wicked_pdf/commit/4f458597d6bc8d9480ea1b12ba9b2c4bcfafa8c3
make it work with heroku:
https://github.com/corsego/howto-wicked_pdf/commit/794dc350499aa5e5421a9bf5d6c4e9657f7924c0

0:00 Installation, Basic usecases
14:05 Send PDF as attachment
18:35 wicked_pdf on heroku