Hi Raheel Farooq,
You can do this using subscription on tableau online .You can subscribe the whole workbook as a pdf but about sending the mail automatically ,you can send mails to tableau online users only .
If you want to have a predefined body for that mail you can have it .
Click on the message and write the predefined body for this mail.
Please mark it right and helpful if this serves your purpose ,so that others can also get benefited .
download all dashboards via tabcmd and use any command line tool to send mail.
We can create one batch file with tabcmd pdf download and send emails and automate with task scheduler.
Tableau server direct subscriptions will send snapshots.
BI, Aspire Systems (India) Pvt Ltd