Whohow.io is a free service that allows you track and breadcrumb when someone opens your emails, links (to websites, shared files on Dropbox and Onedrive, etc), and documents (Office 365, Google Docs, etc.). Please use this service responsibly.
You must have a Google Account to login to use the service. This service does not store any sensitive data.
Place an invisible pixel in your emails and documents. Tracks when a user opens the document or email.
Track when a user clicks on a link. You choose where you want the link to forward to. This is great for shared Dropbox, Google Docs, and Office 365 docs.
Create a customer image URL from an image that is already available on the internet. Embed that image in your docs or emails and track when someone views it.
Place a confidential data / data disclaimer at the bottom of your email. When the disclaimer is viewed, usage will be tracked.