Which product are you using?
PDF.js Express Plus
PDF.js Express Version
latest version
Detailed description of issue
Need to find a way to select an area on the pdf and zoom that area only to fill the view. So, a user will click on a zoom tool, and then select an area on the pdf by pressing mouse left button and when released, that area will be zoom in.
Similarly, there is another tool , which when clicked, will fit the page to fill the view.