Following is a list of documentation available in the downloaded Zen Cart ZIP.
Click the link to open.

About Zen Cart™

1. Read me first -- Installation

2. Read me first -- Upgrading

3. Configuring PayPal IPN

4. Customizing HTML Email Templates

5. Security - Securing Your Site

6. What's New in v1.2.6

7. Changelog for v1.2.6

8. Summary/Explanation of Product Types