With Build a Flipbook visitors can pick out relevant pages in the Flipbook and in that way create a separate publication - only containing selected pages.

Afterwards, the user can share the customized catalog in an email.

While on the Flipbook, your visitors can now select 'Build your own Flipbook':

From there, they can choose the pages to use in their own Flipbook:

From there, they can select what channel to share their own Flipbook in:

The channels you can select to share from, are determined from what channels you've enabled under Share optimization. See more on that here: