This command will identify all OOXML files such as .xlsx or .docx in a directory recursively using the file command (looking for application/vnd.openxmlformats-officedocument MIME types) and move those to a different directory.
mkdir -p ../Documents && find . -type f -exec sh -c '
case $( file -bi "$1" ) in (application/vnd.openxmlformats-officedocument*) exit 0; esac
exit 1' sh {} \; -exec mv -v --backup=numbered {} ../Documents \;
Based on this StackExchange post. Also see How to move all images to other directory based on file content, ignoring the filename and How to move all videos to other directory based on file content, ignoring the filename and How to move all PDF files to other directory based on file content, ignoring the filename