Support for exporting WMF (Windows Metafile) and EMF (Enhanced Metafile) images should be implemented for the Net Standard version.
To allow the library to export such images you can use the extensibility point for providing a custom implementation of the JpegImageConverterBase. More information and examples can be found in the PdfProcessing`s Cross-Platform Support help and Create Custom JpegImageConverter in .Net Standard knowledge base articles.