This is one of the key skills for a software Project Manager. Having the ace of spades in bluff up your sleeve means you don’t actually have to know everything about your project or, indeed, anything about anyone else’s.
You only need to bluff enough to get you beyond the current situation, then you can find out the real facts, or assign the responsibility to someone else. So, the trick is not to appear phased by anything and to give the impression that you know all about the problem/situation/issue, but avoid coming up with any radical solutions until you have time to think it through properly. Remember, if you overdo it, you may end up left holding the baby.
Using a few basic rules of engagement, you can bluff your way through progress meetings, planning meeting, budget meetings etc.
The more experience you get in the software game, the better your ability to bluff will become. It’s an experience thing, but make sure you practice.