PFM is read-only for ISO images.
I use it all the time for ISOs that don't need to be "inserted" into a drive, (eg. DVD Video).
It's a simple matter of right-click->Quick Mount and then double-click the ISO to access the files via Explorer/DOpus. Applications can directly access the files in the ISO but will have to save any changes to somewhere else, (as is the case for a real CD/DVD ROM).
If you need to mount the ISO to a drive letter, then there is also Microsoft's own free VirtualCD Control Panel
. Standalone, (un)install the driver, (un)mount images - pretty basic but good to carry around on your Flash drive.