Hi John,
works but PDFXchange still complaints about xref structure.
I think hacking the PDF really is the hard way. Also I found out that the javascript-Button doesn't work in Foxit-Reader (Scribus and Openoffice PDFs).
But here is a solution that works in PDFXchange and Foxit Reader. AND is native OpenOffice way.
It doesn't send back the whole PDF but the form_data (.fdf) that can easily be read with a text editor.
https://www.libreoffice-forum.de/viewto ... 6379#p8223
You can create a button in OO, double click on it and set its action property to "submit form".
To assign your email address right click on the button and choose "Form"

- Form-properties.PNG (18.37 KiB) Viewed 19694 times
Now when the button is clicked in the PDF, the email program will be started with the email-address and the form-data.fdf attached.
The subject and body text can't be set. They will be filled by the PDF-Reader. It mostly reads:
subject: Data from "pdfname.pdf"
body: The attached file contains data which was filled into a form...
I simply reattach the files from the other forum here.