You can configure the estimate auto-sender to include a PDF copy of the Estimate as an attachment every time an Estimate is sent.

Navigate to your Estimates, Proposals or Quotations board as shown below.

Click 'Show Menu' as shown below.

Click 'Automated Events' as shown below.

Click 'Estimate auto-sender' as shown below.

Scroll down past the email and locate the attachments section as shown below.

Check the 'PDF File' box so that it is ticked, then click the 'Save' button.

Your customers will now receive a PDF copy of the estimate when it is marked as 'Sent.'