Thanks for your fast answer Cathal!
I have been "playing" around with the footnote deal.
One solution I have found to edit Headers & footnotes is using "Custom properties" inserted on footnotes and headers of a template documents and then, edit them via DocX Library. Seems to work fine.
About the "image location" problem, I Google "using relative path on Word" (because I want to link a image into the .docx file, at precise location, but the file must be readed always from the .docx containig folder). I found this link:
I'm now trying to use "Custom properties" with DocX Library to change the image filename.
Hope your DocX keep updating!