"AD" could stand for "Anwendungshinweise für den Dachdecker", which translates to "Application Instructions for Roofers" in English. "2000" might refer to the year 2000. "Merkblatt" means a leaflet or guideline. "W1" could be a specific version or number. "Free" might be part of the title or a typo. Maybe it's "Ad 2000 Merkblatt W1" and "Free" refers to the document being available for free download?