Mike was telling us:
Mike nous racontait que :

It is not a case of losing formatting as it is a case of inserting a file
with wide margins in a file that has very narrow margins...

It is especially obvious with regard to you picture because you set the
picture wrapping to "Square". In the original document, the right margin is
wide so there cannot be any text to the right of the picture. Once you
insert the file in the document created from the tempalte with narrow
margins, the picture is placed in the same position (relative to the right
left margin, or "Column", but now the left margin is so narrow, that some
text fits to the right of the picture, thus apparently throwing your
formatting out of whack...
The same happens with paragraphs that are set to a negative indents. In a
document with wide margins, the text can be easily read, even if it
overflows in the margin area, but once inserted in a narrow-margin document,
some of the text may disappear off the page if the negative indent is wider
than the margin itself.

So, either you make sure that your document have the same margin width, or
you take steps to prevent problem, like not using negative indents and
setting the wrapping to "Square" and "Left Only" (Text Wrapping tab of the
Advanced button found on the Layout Tab of the Picture Format dialog in
Word). But even then, if you use different margins, the amount of ext above
and below the picture may change enough that the result will be
unsatisfactory.