WEBIN have option to send this offer to customer which is related. Also the PDF offer will be attached to the email. If you want to do not attach the PDF offer simple uncheck the checkbox Attach Offer PDF
After sending the offer to the customer if you want to send again the estimate there will be another email content. Becuase the initial offer is already sent. Now the customer maybe want the offer again and in all cases this content will be different. Go to Setup-> Email Templates -> Estimate Already Send to Client to edit the email content when sending the estimate to your customer for second time.
By default all contacts with permission offer will be selected you can adjust to your needs.