The Project Explorer is the control center for your Help+Manual projects. It displays the structure of your project with the Table of Contents (TOC), all your topic files (including those not in the TOC), additional files associated with your project (Baggage Files) and all the configuration settings saved with your project (Configuration).  

You can open multiple projects at the same time. Each project has its own full entry in the Project Explorer. Working in the Project Explorer you can copy and paste single and multiple topics and chapters both within your project and between different projects.

In addition to this, you can also open Help+Manual more than once and have multiple projects open in the different instances of the program. If you are working in the uncompressed HMXP format you can also have the same project open multiple times in different instances of the program.