what are the widest 700c available(with kevlar)?
Yes, it is generally possible to install wider tires that those which came with a bike.

The limiting factors are the clearance available in the forks and frame. The chainstays/bottom bracket area is usually the most constricted area.

The rims will also have a maximum size of tire they can support, but the frame clearance is likely a more limiting factor.

If you have 38mm tires now, you can probably step up to 40 or 42mm.