[mplanchard]

If you are using SolidWorks, open the part with FeatureWorks checked in Tools, Add Ins. That way you can select the geometry to be converted to become parametric. I usually select hole that are used for mounting or the overall extruded profile. You dont want to convert the entire model for they get too big.

You can also use Convert Entities to extract geometry into a sketch. Once SolidWorks sees it, the sketch will be able to be constained.

Marie