DWF files are web based drawing files that can display their drawing without AutoCAD.
TPC does not currently support DWF files.
DWF files can not be opened and edited in AutoCAD like a DWG file can. They are meant to display the drawing like it would be displayed inside AutoCAD. As such, they can render the drawing but can not edit it. They are used to share drawings in their rendered format without AutoCAD.
To view a DWF file, you will need a DWF viewer, such as AutoDesk's DWF Composer. Free DWF viewers are available on the web by searching for the keywords DWF and Viewer.
DWG Files
Exporting DWF Files
DWF Support
Layers
Working with Drawing Objects
Converting Drawing Objects to Survey Points