With the Combine tool, you can combine open documents into a multi-page document and optionally apply variable data. The resulting file is automatically nested for minimum media usage applying an outline-based positioning
How to merge documents
1. Choose File > Combine. The Combine dialog is displayed.
2. Activate the option Combine Opened Files into Multipage Document.
3. Enter a name for the resulting document.
4. Click OK.
All opened files are merged into a new multi-page document.