The Filled Surface 
feature constructs a surface patch with any number of sides, within a boundary defined by existing model edges, sketches, or curves, including composite curves.
You can use this feature to construct a surface to fill a gap in a model. You can use the
Filled Surface tool in these cases:
- Correct a part that does not import correctly into SOLIDWORKS (where there are missing faces).
-
Fill the holes in a part used for core and cavity molding.
-
Construct a surface for industrial design applications.
-
Create a solid.
Include features as separate entities, or merge those features.
To create a filled surface, click Filled Surface on the Surfaces toolbar, or click , set the PropertyManager options, and click OK 
.