Hi Michiel van der Velden,
I have no access to Solidworks, but on their website, they have a list of formats:
https://www.spatial.com/resources/glossary/solid-works-file-format
DXF should work. It is one of the older 3D formats. Sent a small test first and make sure (in a two-way communication) that the file is working correctly. Molds can be expensive.
Native engineering CAD formats are not polygon-based; they are more a mathematical description of the shape in question.
This kind of data could be compared to an Illustrator file or a spline in C4D. With a few points, a possible complex shape can be set up.
In contrast are pixel-based images, which can be seen as an example for polygon-based models. It is easy to turn an illustrator file into a pixel-based image, but the other way around is not that simple, and the results are not that nice, to say the least.
In CAD applications, this (path to pixel) is going from a nearly perfect shape to a limited resolution based on polygons. Similar to the Adaptive mode in Splines.
Any 3D shape in Cinema 4D is based on segments or polygons, not based on a mathematical definition. Whereby the Volume might sit between chairs here. But that is not helping here.
Export a DXF and reimport it into a new scene.
My best wishes for your project
