I am trying to convert an imported file (with surfaces) to a solid model.  I have limited knowledge of any of the features that are supposed to resolve this issue.  I have tried "Knit Surface", "Thicken", "Filled Surface",.. none of which are helping me with this issue.

The file shows all of the external features.  However, I need to make a cutout in this model and when I attempt to do so, I do not get anywhere.  I am unable to "Extrude-Cut".  When I do a section of the part, I can see that it is hollow.

Any input/thoughts??

Thank you,

Tommy