how to change the default preview PDF on outlook

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how to change the default preview PDF on outlook

Matheus Toscano 20

I work in IT support, and a colleague of mine mentioned that the default PDF preview in Outlook has changed for her. Previously, the document would automatically open zoomed in, making it easier to read. Now, she has to manually click “100%” in the lower-right corner of the preview panel each time she opens a PDF. It may seem like a small issue, but since she opens hundreds of PDFs every day, it becomes quite an annoyance. How can I change the default zoom level for the PDF preview in Outlook?

She uses outlook web.

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Francisco Montilla 18,090 Independent Advisor

Hello,

In Outlook on the web there is currently no setting that lets you set or remember a default zoom for the built-in PDF previewer. Microsoft's web viewer always resets its zoom and there is no user or admin toggle to persist 100% or Fit to page.

The workaround is to bypass the OWA previewer so the file opens in your browser's native PDF handler, where zoom can be controlled persistently. In practice that means opening the attachment without using the inline preview.

In OWA, open the message, select the attachment's overflow menu, choose Download, then open the file so it loads in the browser's PDF viewer tab. In Microsoft Edge you can set a default page zoom that will stick across tabs by going to Settings > Appearance > Page zoom and selecting the level you want. This does apply to all sites, but it avoids having to hit 100% on every PDF preview.

If you want, I can tailor a quick click path for your colleague's browser and OWA layout, but the essence is the same. The web previewer itself cannot be told to default to 100% today.

Matheus Toscano 20 Reputation points

2025-10-23T13:39:28.4433333+00:00

Hello,

Thank you for the clarification — I’ll consider your suggestions. But do you know why the default PDF preview changed? It wasn’t like this before. My colleague reported that it changed about two months ago. I tried to find a solution but couldn’t. Strangely, about two weeks later, the issue seemed to resolve itself — the preview mode was automatically zoomed in again. And now it changed once again.

Maybe Outlook changed it in an update?
Francisco Montilla 18,090 Reputation points Independent Advisor

2025-10-23T19:37:41.4733333+00:00

Outlook on the web's PDF preview is a cloud service that Microsoft changes on the server side, so behavior like the default zoom can flip without any change on the user's PC. Microsoft rolls out and even rolls back these viewer changes gradually using feature flags and Targeted release rings, which is why your colleague saw 100%, then Fit to page, then 100% again over a few weeks. This kind of flip-flop is typical when a change is being flighted or hot-fixed.

The timing you describe matches recent reports from other admins that OWA's PDF preview suddenly stopped remembering the prior zoom and started opening at a different default, then later reverted.

There is no user or admin toggle today to set a persistent default zoom in OWA's built-in previewer.

Microsoft's guidance covers how to preview attachments in OWA but does not expose a zoom preference, and the PDF/file viewer Microsoft uses across OneDrive and SharePoint is being actively updated, which can surface in OWA attachments too.

If you want to reduce this churn for that user, the one actionable lever you do have is release cadence. Check whether the user or your tenant is on Targeted release, because those users see features while Microsoft is still experimenting. Moving the affected user to Standard release typically stabilizes behavior until the change completes its worldwide rollout. You can verify and change this in the Microsoft 365 admin center under Settings > Organization profile > Release preferences.

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