Technical Explanation for Priority Increase

The current Blazor PDFViewer does not support pinch-to-zoom on mobile devices, even though the underlying rendering engine (pdf.js) natively supports gesture-based zooming. This means that a core browser interaction is being blocked at the component layer rather than by technical limitations of the PDF technology itself.

Key Technical Points

1. pdf.js supports pinch-to-zoom out of the box.
   The Blazor PDFViewer disables or does not expose this functionality. This is an artificial limitation introduced by the Telerik component.

2. touch-action is not the issue.
   Allowing gesture events with CSS does not enable pinch-zoom because the PDFViewer does not implement event listeners for gesturestart, gesturechange, or pointer events required for pinch processing.

3. The PDFViewer only exposes zoom via a toolbar dropdown, which:

   • is not accessible when viewing large documents

   • is not intuitive on mobile

   • is not aligned with standard mobile interaction patterns

4. The absence of mobile zooming makes the component effectively unusable for any document containing:

   • dense text

   • multi-column layouts

   • newspaper or magazine pages

   • technical manuals or PDFs with small fonts

5. This is not a UX improvement request but a core functional requirement for mobile use.
   Every modern mobile PDF viewer (Chrome, Safari, iOS Viewer, Adobe, etc.) supports pinch-to-zoom as a baseline interaction.

Business Impact

We produce and distribute a digital newspaper with thousands of readers who primarily use mobile devices. Without intuitive pinch-zoom, the PDFViewer fails to meet basic usability standards, forcing us to adopt a third-party PDF component despite being long-term Telerik subscribers.

Requested Action

Please enable native pinch-to-zoom support by exposing the existing pdf.js gesture-zoom functionality through the Blazor PDFViewer. This has been requested for several years and is essential for mobile usability.

I have been trying for three years to make you understand that the PDF viewer on mobile is almost unusable because you cannot zoom using pinching, the normal way of zooming on mobile devices. It is truly incomprehensible to me that this still hasn’t been addressed, especially since pdf.js, your underlying library, fully supports it.

There has already been a ticket open for a long time, but you simply don’t listen to what I’m saying:
THE PDF VIEWER CANNOT BE USED ON MOBILE!

https://feedback.telerik.com/aspnet-core-ui/1481051-zoom-in-out-file-using-the-build-in-zoom-functionality-of-the-pdfviewer-when-zooming-with-two-fingers

And try zooming on mobile in your own sample:
https://www.telerik.com/blazor-ui/documentation/components/pdfviewer/overview

We produce a newspaper, which means a lot of text on a single page, so our customers must be able to zoom in and out quickly, easily and intuitively. That is exactly why pinching was invented. The dropdown is not convenient when you are in the middle of a page and certainly not the desired or intuitive way of zooming on mobile.

I notice this more often with Telerik. Very simple, practical issues are not being addressed. I call these the “quick wins” that actually keep customers engaged.

It would be great if you could finally fix this and make the Blazor PDF Viewer usable on mobile. In the meantime, we are forced to use another PDF component for mobile. That can’t be the intention, right?

Can you please give this ticket extra priority, considering we have already been waiting five years (!) for this component to become functional?

Have you ever tried to read a PDF on a mobile device yourself using the PDV Viewer for Blazor?

For instance a folder or newspaper? I guess not otherwise you would not give a reaction like this.

The intuitive thing using mobiles and zoom is to pinch, that is why pinching was invented.

Pdf.Js does support that but somehow the Blazor implementation of Telerik does not use that functionality.

On mobile devices the zoom buttons are very small and not really usable.

So please add pinching functionality to the PDF viewer otherwise the PDF viewer is nearly useless on mobile devices.

We still need this...

I would like to state that the PDF viewer component is un-usable on mobile devices since the lack of pinch support.
Please add pinching!