I assume 'diff' is short for difference so you are looking for something that compares 2 drawings.
I've never come across anything that does this, although I have heard of such products.
As for the one you mention...
"Revu automatically compares two PDF drawings and marks the differences with clouds"
The only way to tell how useful it is, is to trial it.
bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.