Octopus Overlords

Can someone recommend a tool/extension/software/whatever that can check an online PDF on a schedule and alert me if there are changes from last time? It's for work but needs to be free... I tried distill.io, which claimed it can check a PDF page but it errors out when it tries (so, like, if I feed it a link to the TDaP VIS on the CDC website: http://www.cdc.gov/vaccines/hcp/vis/vis ... s/tdap.pdf - I need an alert if the revision date changes).

I used Wachete. The catch is the free tier only checks every 24 hours. If you need more frequent checking, you need to pay.

I'll give it a shot, thanks!