You can use
instance. setMaxZoomLevel(zoomLevel) to set the minimal and the maximum zoom level.
instance.setMinZoomLevel('10%'); // or setMinZoomLevel(0.1)
instance.setMaxZoomLevel('150%'); // or setMaxZoomLevel(1.5)
Please look at this API doc for detail: PDFTron WebViewer Class: WebViewerInstance
Let us know if this helps.
PDFTron Systems, Inc.
CONFIDENTIALITY NOTICE: This message (and any attachment to it) is intended only for the use of the individual or entity to which it is addressed in the header, and may contain information that is privileged, confidential and exempt from disclosure under applicable law. Any reproduction, distribution, modification or use of the contents of this message (and any attachment to it) by any individual or entity other than the intended recipient is prohibited. If you have received this communication in error, please notify us immediately and delete the original.