EchoMark uses multiple marking methods that allow us to protect against complete (entire PDF or .EML file) and partial (images of pages or messages) leaks.
EchoMark can generate an unlimited number of unique PDFs using our Digital Stamp method (which protects your content against full-PDF or full-EML leaks) but we are currently limited in the number of unique invisible watermarks that we can apply to content. This means that there are limits to the number of unique copies that we can create for any given message or PDF page and thus limits to our ability to detect matches on partial leaks.
You can read more about these limits in our article on Invisible Watermark and assess your specific content using the product's Mark Report.