Once you have a document ready to share with your customer, here's how to do it:
Click the Export/Share button at the top right, on the document page.
Clicking it will reveal 3 options to share:
Download a PDF.
A share link that you can copy send to them.
The option to your customer's email and D3M will send an email on your behalf giving your customer a personal link showing you when they have accessed the document.