Dexter is a service that allows you to reconstruct data from graphs you only have in PDF or as an image.
Before you can upload your source, please give your data some name. You can use that name later to do further extraction, to revisit your work, or to pass it on to colleagues.
It currently requires support for Java applets in your browser, which is becoming uncommon in 2019. We will switch to Java web start. Until then, if it doesn't work for you any more, this blog post discusses alternatives.