How to manipulate OptionButton / Radio button on docx with Open XML? (C#)

Question

I have a.docx template that I need to fill with C#. This template has some sections with radio button groups, just like this:

I'm using open XML, I've inspected the xml and I think I found the radio buttons:

          <w:p w14:paraId="6E7C5D2C" w14:textId="2740F2E7" w:rsidR="0085589C" w:rsidRPr="00055073" w:rsidRDefault="0085589C" w:rsidP="00465D62">
              <w:r>
                 <w:object w:dxaOrig="225" w:dyaOrig="225" w14:anchorId="28DEEE36">
                    <v:shape id="_x0000_i1053" type="#_x0000_t75" style="width:78pt;height:17.25pt" o:ole="">
                       <v:imagedata r:id="rId15" o:title="" />
                    </v:shape>
                    <w:control r:id="rId16" w:name="OptionButton3" w:shapeid="_x0000_i1053" />
                 </w:object>
              </w:r>
           </w:p>

I can't figure out how to manipulate these elements with C#. I tried to iterate through doc elements and found an element with name OptionButton of type Control, but I haven't found a property or method that allows me to manipulate its value:

Could someone help me with this, please?

Thank you.

Answer 1

The Option Buttons shown in the question are ActiveX controls, originally designed to be used in VBA UserForms. Office document surfaces were then adapted to allow them to be used in documents, retaining their programming interface.

ActiveX controls are not defined by Office Open XML. As with all things VBA, they remain in the proprietary binary format (pre-Office 2007).

Here's an extract of the Word Open XML for an Option button:

<pkg:part pkg:name="/word/activeX/activeX1.bin" pkg:contentType="application/vnd.ms-office.activeX">
<pkg:binaryData>0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAAAAAABAAAAAQAAAAAAAAAA
EAAAAgAAAAEAAAD+////AAAAAAAAAAD/////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////

In order to "read" this kind of content it would be necessary to have access to and understand the Word and Office binary file formats.

Reference, for example: https://docs.microsoft.com/en-us/openspecs/office_file_formats/ms-doc/ccd7b486-7881-484c-a137-51170af7cc22