Until recently Autodesk has not developed their free DWFx/DWF viewer, Design Review, past the 2013 version. It was unfortunate, because it was a great viewer and markup tool for DWF and DWFx files. "Was" is not quite correct, though. Even though development ceased at the 2013 version, it has always still been available for download. However I noticed over the years that a problem cropped up with the markup functionality between Design Review and Revit. When linking markups into a Revit file, they started becoming registered improperly, so that the markups were not appearing on the sheet in Revit where they were actually created in Design Review.
Speculation was that Autodesk was going to eventually replace Design Review with the browser based Large Model Viewer, which also has markup capabilities, but still doesn't have everything that Design Review offers.
However, there is now an updated version of Design Review, and in my preliminary testing, not only does it have all of the functionality of the previous version, but the DWF Markup registration issue seems to have been fixed. Again, it's FREE - you can download it here.