Have you ever clicked a PDF… and the wrong app opened? It’s a small thing, but it wastes time. Maybe your browser grabs every PDF. Maybe Preview or Edge keeps taking over. Or maybe you just want a free PDF viewer that’s fast and simple.

Good news: you can fix this in a minute or two. Below is a friendly, step‑by‑step guide on how to change default PDF viewer on every major platform, plus quick browser tweaks and a reliable pdf viewer online if you just need to open a file right now.

Quick note: I’ll show the official steps and link to trusted sources for each platform.

TL;DR: The 10‑Minute Fix

• Windows 11/10: Settings → Apps → Default apps → search “.pdf” → pick your app.

• macOS: Finder → right‑click a PDF → Get Info → Open with → choose app → Change All.

• Chrome: Settings → Privacy & security → Site settings → PDF documents → choose to open in Chrome or download/open with your system PDF viewer.

• Edge: Settings → Cookies and site permissions → PDF documents → enable Always open PDFs in external applications (uses your system PDF viewer).

• Firefox: Settings → General → Applications → Portable Document Format (PDF) → choose Open in Firefox, Always ask, or Use (your app).

• Android: Settings → Apps → Default apps (or Open by default) → set/clear defaults; next time you open a PDF, pick your preferred PDF viewer and tap Always.

• iPhone/iPad: There isn’t a system‑wide default for PDFs; open in Files or Books, or Share to your chosen pdf viewer tool. iOS 18 adds “Default Apps” for things like browser and email, but not PDFs.

Why Does this Keep Changing?

A quick story: last month I opened a contract in Windows and it launched in my browser, not my editor. Turned out a browser update reset my defaults. It happens after OS updates, new app installs, or policy changes at work.

That’s why the fix matters: set the default once, then double‑check your browser behavior so PDFs don’t “steal focus” again.

Step‑by‑Step: Change Your Default PDF Viewer

Windows 11 & Windows 10 (Fastest Way)

1. Press Windows + I to open Settings.
2. Go to Apps → Default apps.
3. In the search box, type .pdf.
4. Click the current app and choose the PDF viewer you want. That’s it.

Pro tip: You can also right‑click any PDF → Open with → Choose another app → select your pdf viewer tool and tick Always. This sets it for all PDFs. (Windows uses the same underlying file association.)

If Edge keeps opening PDFs from the web, flip its built‑in PDF setting (details in the Edge section below) so your chosen PDF viewer handles files.

macOS (Finder’s “Change All” switch)

1. In Finder, right‑click any PDF → Get Info.
2. Expand Open with and choose your app (Preview, Acrobat, your editor, etc.).
3. Click Change All so every PDF opens with that PDF viewer.

This is the most reliable way on a Mac. It takes 20 seconds and sticks across reboots. If your free PDF viewer app updates later, just repeat these steps to re‑affirm the default.

Android (set or clear the default)

Android’s menus vary a bit by device, but the idea is the same:

• Set a default: Open Settings → Apps → Default apps. When you open a PDF the next time, Android will let you pick a PDF viewer and choose Always.

• Clear a stubborn default: Settings → Apps → (Your current PDF app) → Open by default → Clear defaults. Then open a PDF and set your preferred pdf viewer tool as Always.

If your phone doesn’t show a direct “PDF” default, that’s normal—defaults are per action/type. Clearing defaults forces Android to ask again.

iPhone & iPad (what you can—and can’t—set)

Apple now lets you set some Default Apps (browser, email, calling, etc.) in Settings → Apps → Default Apps on iOS 18.2 and later. But there’s still no system switch for “default PDF app.” You open PDFs in Files or Books, or tap Share → Open in to send a PDF to your favorite pdf viewer tool.

If you read a lot on mobile, Books is a built‑in free PDF viewer with markup tools, and it syncs with iCloud.

Don’t forget the browser: Chrome, Edge, and Firefox

Sometimes your system default is correct, but the browser still opens PDFs in a tab. Here’s how to make browsers respect your choice (or use their viewer when you want).

Google Chrome

• Go to Settings → Privacy & security → Site settings → Additional content settings → PDF documents.
• Pick whether to open PDFs in Chrome (Chrome’s built‑in PDF viewer) or download/open with your system PDF viewer.
  

Chrome’s viewer is a handy free PDF viewer with search, annotate, and sign tools—great when you just need speed.

Microsoft Edge

• Open Settings → Cookies and site permissions → PDF documents.
• Turn on Always open PDFs in external applications to push files to your chosen system PDF viewer. (Admins can enforce this via the AlwaysOpenPdfExternally policy.)

Edge also has a strong built‑in viewer (now powered by Adobe tech), but if you prefer your editor, this switch makes it stick.

Mozilla Firefox

• Open Settings → General → Applications.
• In Content Type, find Portable Document Format (PDF), then choose:
  • Open in Firefox (built‑in PDF viewer)
  • Use [Your App] (system PDF viewer)
  • Always ask (lets you pick each time)
    

Common “Why won’t it stick?” fixes

• Browser still takes over: Revisit the browser section above and make sure the built‑in viewer is off or set to Always open externally (Edge) so your pdf viewer tool takes control.
• Work laptop? IT policies may lock file associations. If so, you’ll need admin help. (Edge’s PDF policies are a common example in managed environments.)
• New app installed: Some apps ask to be the default PDF viewer during setup. If things change after an install, just re‑apply the steps for Windows or macOS.
  

Quick checklist: Your “set‑it‑once” plan

1. Pick your primary app (your editor or a free PDF viewer that you trust).
2. Set the system default (Windows/macOS steps above).
3. Tune your browser (Chrome/Edge/Firefox) so it doesn’t override your choice.
4. On Android, clear any old defaults and set your preferred pdf viewer tool.
5. On iPhone/iPad, open in Files/Books, or share to your app of choice—there’s no system‑wide PDF default.
   

Real‑World Example (and a time‑saving tip)

A freelancer I helped last week was juggling proposals between Windows and a Chromebook. PDFs kept opening in different apps, and comments went missing. We set the Windows default to her editor, told Chrome to download PDFs instead of previewing, and used a pdf viewer online when she was on the go. Result: one consistent workflow, fewer errors, and saved time on every client doc.

FAQs

What’s the best free PDF viewer?

You already have a few: Preview on Mac, Chrome’s PDF viewer, and Firefox’s viewer are all fast and free. Edge also has a strong built‑in viewer. If you need to edit or sign often, you may prefer a dedicated pdf viewer tool with editing features.

Is a pdf viewer online safe to use?

Stick to trusted tools and avoid uploading sensitive files unless the site states strong privacy and security. For anything private, use your local PDF viewer or an encrypted workflow.

Why does Edge open PDFs even after I change defaults?

Edge can ignore the system default if its internal viewer is on. Turn on Always open PDFs in external applications so Windows hands files to your chosen PDF viewer.

Can I set a default PDF viewer on my iPhone?

Not system‑wide. You can open in Files/Books or share to another app. iOS 18.2 adds a Default Apps menu for things like browser and email, but not PDFs.

Does Chrome’s viewer count as a free PDF viewer?

Yes—Chrome includes a built-in PDF viewer with search, annotation, and sign. You can keep it on for quick reads, or switch it off so your system PDF viewer opens files.

Wrap‑up

Changing the default takes a minute, but it pays off every day. Set your system default PDF viewer, tune your browser so it behaves, and you’re done. If you’re bouncing between devices, keep one trusted free PDF viewer as your “home base,” and use a pdf viewer online when you just need to peek at a file.