This does the expected on my end with doc-view-scale-internally to nil:
when visiting a djvu file and zooming in, it regenerates the images;
when visiting a docx file and zooming in, it modifies the :width image
property (i.e., no regeneration).

>>> I wasn't thinking of duplicating the code, but of rethinking the naming
>>> a bit.  I think what we meant by "pdf->png" is actually the process that
>>> extracts pages (which just happened to use the PNG format and now can
>>> also use the SVG format).
>
>> Indeed, it is a misleading name.  This change will have to go to master,
>> I believe?  I have to look around a bit more to see where the function
>> is being used.
>> There's also the fact that there's more than one more program that can
>> generate SVG files (as Gregory pointed out in this thread) so it might
>> be nice to have pdf->png and pdf->svg "function variables" and a "super
>> function" that actually does the job.  Hopefully, this will allow to
>> fall back gracefully to PNG if SVG generation is faulty.
>
> Indeed, I think there's some cleanup/orthogonalization in order here.

When I have more time and familiarity, I will try to give this a shot.

>         Stefan