Issuu is a service that allows you to upload a PDF document to their site, and then display that PDF as a flipbook. Once you've created your flipbook, go to https://help.issuu.com/hc/en-us/articles/211809598-Embedding-Your-Own-Publication to get an embed code.
To add an embed element to your Composer page:
Select an Embed element.
Open the settings of the element, and paste the embed code from Issuu into the available space. Be sure to toggle the header of the element in the element settings to avoid the "Embed" header appearing on the page.
Save the element and view your page.