As of version 4.0, the User Guide for TPE has been incorporated into the Help Center itself. Please see the articles under the General Section.
The Quick Start Guide which is shown in the app is available directly here: Version 4.1
If you prefer to have the documentation in PDF form, a consolidated PDF containing a snapshot of the Quick Start Guide and articles in the General Section of this site for TPE for iOS is available here:
This is current for version 4.1 of the app.