What originally generated or opened your SDFA file?
Ensure your version of Exocad is updated, as newer versions sometimes offer better handling of older or encrypted files. Summary Table: SDFA to STL Conversion Reliability Ease of Use Exocad "Save As" Exocad Merge & Export 3Shape Converter
Because SDFA files are intentionally locked, converting them requires utilizing Exocad’s own tools or finding specialized workarounds. Understanding the Formats: SDFA vs. STL
Because it contains complex data about physics and motion, it is not a pure 3D mesh file. What is an STL File?
Are you trying to export a specific or a completed crown design for 3D printing?