Can the GM do this while playing?

Greetings. This is a simple question which is pretty obvious but we have not started yet and well I thought I would ask.  We are doing a more role play and 'investigative' campaign with a reduced focus on combat but its still there. I want to be able to roll my players skill checks for various skills as the GM and thus role play out some various results. For example:  Keith has a Diplomacy of 3 and needs to succeed (DC 18 on d20) in getting information on how to write complicated macros.  I want to roll his Diplomacy skill right off the sheet. Its ok if the players see the results of this roll and I'd also like to see the DC or target number that roll was trying to achieve.  Can I also tie a target DC to that roll as well? 

It depends; where are you getting the target DC? For example, BLUFF is directly countered by SENSE MOTIVE, both skills on a character sheet. One could write a macro similar to this: BOB makes a BLUFF check against SUE: [[1d20+@{BOB|Bluff}]] vs [[1d20+@{SUE|Sense_Motive}]] This would require, of course, that such Attributes exist on each character's sheet. Alternately, you could make a macro that queries the user to input a given value: [[1d20+@{BOB|Bluff}]] vs [[?{Amount|0}]] These are simple versions, of course, for demonstration purposes. Adding in a comparison is relatively easy, if you simply wish to display a yes/no result instead of the actual numbers.

The DC comes from a module So it reads If Aaron succeeds on a Survival DC 18 check he will get information and be able to track Kobolds under the Ossuary. 

...hey...

You are Aaron are excellent NPC examples. In this case what I wanted to know if I there was a way to display in chat both the roll and its success or failure against a show value check which in path finder is called a difficulty check (DC). 

So following that if I roll Keiths diplomacy and it is a 13+3 = 16 and the DC 18 (fail) does roll20 show that or do I need to make some kind of macro to do that?

Check out Powercards Larsenex. They can work miracles. 

Maybe something like Diplomacy Check: [[ @{target|diplomacy}+1d20cs>?{DC?|10} ]] vs DC [[ ?{DC?|10}  ]]