Take a look at ChartJS widget - https://appstore.home.mendix.com/link/app/1712/
It includes a functionality to export the chart as a base64-encoded image. This you can then use in a pdf.
EDIT: Check in the release notes
The way it works is you connect a string attribute to the widget, and once the widget is rendered this string attribute is set to the base64-encoded image.
You should be able to get it show in the pdf by wrapping it in an img html tag. Just make sure to set the rendering to XHTML. Alternatively use community commons base64decodeToFile to store it (temporarily) in a persistent object then use this in your pdf.
You could also look at JFree Charts module - built for this purpose. It hasn't been updated recently, but may still work.