Describe your proposed improvement and the problem it solves

See #10741. I want to include images in my custom template.openxml. However, images are included using rIds, which point to Relationships defined in /word/_rels/document.xml.rels. For a more detailed example of how this works, consider the Appendix below.

Because I currently have no way of controlling the contents of /word/_rels/document.xml.rels in the output DOCX, I have no way of including images in template.openxml. This could be fixed by including the images in the reference-doc.docx, if pandoc preserved the reference-doc's existing Relationships defined in /word/_rels/document.xml.rels when creating the output DOCX (pandoc currently doesn't do that). I would then have rIds for my images which I could use in template.openxml.

I am not sure if all Relationships from /word/_rels/document.xml.rels should be preserved, but at the very least those of Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/image".

Pandoc already preserves the actual image files in the reference-doc in /word/media/ when creating the output DOCX.

Describe alternatives you've considered

See #10741 for a considered alternative that doesn't actually work.

Appendix: How images are included in Word's OpenXML

When a DOCX contains an image, the corresponding OpenXML in /word/document.xml looks something like this (Word is actually very particular about this and doesn't tolerate the removal of some elements that might seem superfluous to the minimalist OpenXML author):

<w:p>
  <w:r>
    <w:drawing>
      <wp:inline>
        <wp:extent cx="990000" cy="792000"/>
        <wp:docPr id="1" name="Picture 1"/>
        <a:graphic xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main">
          <a:graphicData uri="http://schemas.openxmlformats.org/drawingml/2006/picture">
            <pic:pic xmlns:pic="http://schemas.openxmlformats.org/drawingml/2006/picture">
              <pic:nvPicPr>
                <pic:cNvPr id="0" name="image1.jpg"/>
                <pic:cNvPicPr/>
              </pic:nvPicPr>
              <pic:blipFill>
                <a:blip r:embed="rId8"/>
                <a:stretch>
                  <a:fillRect/>
                </a:stretch>
              </pic:blipFill>
              <pic:spPr>
                <a:xfrm>
                  <a:off x="0" y="0"/>
                  <a:ext cx="990000" cy="792000"/>
                </a:xfrm>
                <a:prstGeom prst="rect">
                  <a:avLst/>
                </a:prstGeom>
              </pic:spPr>
            </pic:pic>
          </a:graphicData>
        </a:graphic>
      </wp:inline>
    </w:drawing>
  </w:r>
</w:p>

The actual image is included in the element <a:blip r:embed="rId1"/>, which references rId8 in this case. This rId is defined in /word/_rels/document.xml.rels (below is only an excerpt of that file):

  <Relationship Id="rId8" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/image" Target="media/image1.png" />

The actual image file resides at /word/media/image1.png, as defined in the Relationship above. Without controlling the contents of /word/_rels/document.xml.rels, one cannot therefore include an image in OpenXML.

Version

Pandoc 3.6.4