Thanks for your inquiry. Please note that Aspose.Words mimics the same behavior as MS Word does. If you perform the same scenario using MS Word, the size of output document will be changed. Aspose.Words does not truncate any content in output document e.g. styles, direct font formatting etc.
The Docx file is ZIP package and you can check the detail of contents in it. Please unzip the output document and check xml documents e.g. document.xml, styles.xml, fontTable.xml etc.