Please note that GroupDocs.Editor supports input controls in WordProcessing documents, including text boxes, date pickers, check boxes, radio buttons, drop down lists etc. They are correctly represented in HTML/CSS during editing.
As we understood from the details you shared, you want not to edit the overall content of a document, but only to full-fill and edit data within form fields. However, at this moment using this approach may not be a good solution, because it is unclear how to gather data, entered by the end-user into the fields, on the server-side.
If you can share more details about your use-case that will be helpful for us, how exactly you want to edit the document and grab user-entered data from form fields on the server-side.