In Version v18.4.0.30 occurs the following error:
System.InvalidCastException: Unable to cast object of type 'System.Xml.Linq.XText' to type 'System.Xml.Linq.XElement'.
at Syncfusion.DocIO.DLS.Convertors.DocxParser.ParseMetaDataProperties(PartContainer partContainer)
at Syncfusion.DocIO.DLS.Convertors.DocxParser.BindCustomXmlData(PartContainer partContainer)
at Syncfusion.DocIO.DLS.Convertors.DocxParser.ParseDocument(Package wordPackage)
at Syncfusion.DocIO.DLS.Convertors.DocxParser.Read(WordDocument document, Boolean isFlatOPC)
at Syncfusion.DocIO.DLS.Convertors.DocxParser.Read(Stream docStream, WordDocument document)
at Syncfusion.DocIO.DLS.WordDocument.OpenDocx(Stream stream)
at Syncfusion.DocIO.DLS.WordDocument.OpenInternal(Stream stream, FormatType formatType, String password)
at Syncfusion.DocIO.DLS.WordDocument.Open(Stream stream, FormatType formatType)
at Syncfusion.DocIO.DLS.WordDocument..ctor(Stream stream, FormatType type)
...
After downgrade the package to v18.3.0.53 my code is working again.