# Adobe PDF Canarytoken
# What is an Adobe PDF Canarytoken
This Canarytoken is a PDF document that will notify you when it has been opened (by reasonably compliant PDF readers). The Canarytoken works by forcing the PDF reader to do a DNS lookup on a unique address (so we can safely tie the resolution to the opening of the Document).
Note: DNS Canarytokens are great to get a beacon out from a heavily filtered network, but lack the granularity of some other Canarytokens. In this case, the best you can hope for is to be aware that the document was opened, and have a rough idea of the source.