I have asked for gerber file from third party for my project.

How can i verify the gerber file.

Use a free viewer like to look at the files. There should be quite a few:
top layer
top paste layer
top stencil layer
bottom layer
bottom paste layer
bottom stencil layer
maybe just outer dimension
drill information
When I create Gerbers in Eagle using the .CAM settings from iteadstudio, I end up with 13 files. I don't recall what the others are without looking.

While there are specific apps available for all of the OS you can also test the compliance of your Gerber files online.
E.g.: or

And there are some more, just use the search function of your browser with the keywords "online, gerber file, preview .."

Another way to view it is to log in to OSHPark and use their system. I find it a very good way of seeing what the PCB will really look like.

One more: