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?

We still need this

Also see this:
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

 

Hai all,

For me it is still complete not understandable that standard pinching zoom for the Blazor PDF viewer for mobile devices is not implemented yet. Just try your own demo on a mobile device and try to zoom the PDF. Totally unusable...

https://demos.telerik.com/blazor-ui/pdfviewer/overview

The standard pdf.js implementation does support pinching, so please, add this to the list so the PDF viewer is usable on mobile. devices. We had to buy another component and check the viewport width so we can present a usable PDF viewer with pinching support for our customers. It is a pity we had to move that road away from Telerik regarding PDF's...

To see what I mean, check: https://bettertyped.github.io/react-zoom-pan-pinch/?path=/story/examples-big-image--big-image

Can I exchange some of my Telerik points for this?

Hai Hristian,

Do you have any clue how other customers use the Blazor PDF viewer on mobile devices since PDF's are not readable by default since it requires extensive zooming before reading is possible?

Regards, Marc

We are now 1.5 years later.. And still the PDF viewer cannot pinch.

When will this be fixed so the PDF viewer can act as a worthy PDF viewer, also suitable for mobile devices?

Pinching of PDF on mobiles is essential...

Please vote!

Hai, is this also fixed in the upcoming release where the Blazor PDF viewer has been rewritten bij Progress?

Megards, Marc