I am also interested in this issue very much. Could anybody give us a hint whether it is possible? Personally, I have to achieve the next goal - while printing document it is needed to print a string from the metadata to a corner of the document.
Printing happens on the client side. That is in your browser. You will need to create a print view of the document with the metadata. The best way is to generate an PDF of the original document including the metadata and let the user download and print it.