Thank you for your feedback.
Autodesk Design Review (ADR) can help you to merge existing DWF files into a new multi-sheet DWF file.
You can download ADR for free from: http://www.autodesk.com/designreview-download.
Once installed, ADR provides two convenient ways to accomplish what you want to do.
One method is to use ADR directly by following these steps :
1. Open ADR with or without loading a DWF file.
2. Drag the DWF files needed to be merged into the thumbnail pallet.
3. Save the new file as a new DWF file.
Thus, multiple DWF files are merged together to be one new DWF file.
Alternatively, use a new Windows Explorer shell extension which is available on DWF files after installing ADR. Please follow these steps:
1. Select the DWF files in Windows Explorer and then right click the mouse inside the selected files.
2. Click on "Merge". Then you can enter the name for a new DWF file in the pop-up dialogue box.
3. All the selected DWF files will be merged together to be one new DWF file.
Please let me know if you need further assistance.