As a publisher, you'll have to enable the download functionality on your publications (see Enabling downloads for your readers) if you'd like your readers to download copies of your publication.
To download publications from the issuu website, all readers will be required to log in.
If you don't want your readers to have to register or log into issuu for this reason, the non-member download functionality allows your readers to download your publications without having to login.
Non-member downloads are only available on the Premium and Optimum plans.
As a Premium/Optimum publisher, you'll have to embed your publications (see How to embed your publication) or use the Shareable Full-Screen Reader link (see How do I get the Shareable Full-Screen Reader link).
After enabling downloads for a publication (on the Premium or Optimum plan), your readers will be able to download a copy of your publication from your embedded and Shareable Full-Screen Readers.