Your image is positioned relative to a paragraph:
<w:drawing>
<wp:anchor distT="0" distB="0" distL="114300" distR="114300" simplePos="0" relativeHeight="251658240" behindDoc="0" locked="0" layoutInCell="1" allowOverlap="1" wp14:anchorId="791936E3" wp14:editId="575B92C8">
<wp:simplePos x="0" y="0"/>
<wp:positionH relativeFrom="column">
<wp:posOffset>5317388</wp:posOffset>
</wp:positionH>
<wp:positionV relativeFrom="paragraph">
<wp:posOffset>-325755</wp:posOffset>
</wp:positionV>
docx4j potential to support stuff like that in PDF output is limited by what XSL FO supports. See docx4j's TextBoxTest class for what we can do with text boxes.
Currently, although we can position some textBoxes; we don't do the same for floating images: https://github.com/plutext/docx4j/issues/127
In the meantime, a possible workaround for some cases (eg float right) is to use a table.
Or possibly, you could try putting the image inside a text box!