As per your link I assumed that you have done following process.
you have created column in your list and same column you have added in the document library.
that means you have created Multi Line of text(with rich text) site column and added same column to list as well as library and you are creating document from template(in template you have added document properties) using SharePoint Designer Workflow.
So the main problem is RichText Field(multi line of text with Rich Text) is not supported in document library.
See below links
https://social.msdn.microsoft.com/Forums/office/en-US/67a70245-cd03-48e1-b0fa-71bbb6a7744d/is-enhanced-rich-text-column-supported-by-document-library?forum=sharepointcustomizationlegacy
https://social.msdn.microsoft.com/Forums/en-US/95a05ae0-5d3b-432f-81bf-1f4a03e9910b/rich-text-column-in-document-library?forum=sharepointcustomizationlegacy
So in short you can not achieve your requirement using this way. You need to use OpenXML or other tool to create word file programmatically.
You can get some idea from "https://html2openxml.codeplex.com/documentation"
Hope it will help to you.