What is the output on IF? Is it LO + RF or LO - RF?
Both, usually. The same mechanism that upconverts also downconverts!
Are the pins bidirectional mixer? means, IF and RF are both IN/OUT pins?
Look at the performance graphs: The isolations specified wouldn't make sense if that wasn't the case.
Basically I want to know if it can act as up and downconverter
Whether RF or IF are higher in frequency is up to you to decide. This is a mixer, not specifically an up- or downconverter. Look up the mathematical theory of mixers – they simply produce sum- and difference-frequencies. With a frequency range so wide, it's not even possible that this device includes any filters to remove either!
How to find IF bandwidth for this mixer? My RF signal has 100 MHz bandwidth and after IF conversion, I need 100 MHz on the new frequency.
You have frequency behaviour graphs. Again, this is a mixer, not a specific downconverter or upconverter. Its bandwidth is its frequency range, where of course you need to watch out for higher-order intermodulations landing in your intended output – but that's not a bandwidth issue of your mixer, but of the signal and LO frequency you feed in.