Most people install Adobe Reader out of habit. The viewer already on the machine usually does everything they need, and starts faster.
Setting the default
| Platform | Where |
|---|---|
| Windows 11 | Settings → Apps → Default apps → search .pdf |
| Windows 10 | Settings → Apps → Default apps → Choose by file type |
| macOS | Select a PDF → Cmd-I → Open with → Change All |
| iOS | No global setting; use Share → Open in |
| Android | Settings → Apps → Default apps, or choose "Always" when prompted |
The macOS step people miss is Change All. Setting "Open with" on a file changes only that file — the button underneath applies it to every PDF, and without pressing it nothing appears to have happened.
When it will not stick
Windows in particular has a habit of reverting the association, and there are a few identifiable causes rather than one general flakiness.
Adobe Reader asks to become the default on update and takes it if the dialog is dismissed carelessly. Feature updates to Windows have reset associations. And an association can become corrupted, in which case setting it appears to succeed and does nothing.
- Turn off Acrobat's default-handler prompt in its preferences, under General.
- Use "Choose default apps by file type" rather than right-click → Open with, which is less durable.
- If it silently fails, the association is corrupted. Setting it to something else, then back, usually clears it.
- In a managed workplace, it may be set by policy and will revert at every login regardless of what you do.
That last one is worth checking early on a work machine, before spending time on the others. If a policy is applying the association, no local setting will hold.
Chrome as a PDF viewer
Chrome opens PDFs in a built-in viewer that is fast, sandboxed and now includes annotation. For reading and light markup it is genuinely sufficient.
It can also be the default application for PDF files on disk, not only for ones encountered on the web — set Chrome as the .pdf handler and double-clicking a file opens it in a browser tab.
- Downloading instead of opening: Settings → Privacy and security → Site settings → Additional content settings → PDF documents → Open PDFs in Chrome.
- Annotation: the toolbar includes drawing and highlighting.
- Forms: basic AcroForm filling works; complex XFA forms do not.
- What it cannot do: merge, split, redact, or handle digital signatures properly.
The security argument for browser viewers is real. PDF rendering has historically been a rich source of vulnerabilities, and Chrome renders in a heavily sandboxed process that is updated far more frequently than a desktop reader most people never update at all.
Preview on macOS does more than people realise
Preview is the reason a Mac user rarely needs to install anything for PDF work. It is not a cut-down viewer; it is a capable editor that happens to be free and pre-installed.
Combining files is the standard example. Open one PDF, show the thumbnail sidebar with Command-Option-2, then drag another PDF file into the sidebar — its pages are inserted at the drop point. Drag to reorder, and save.
- Merge: drag a PDF into another's thumbnail sidebar.
- Split: drag pages out of the sidebar to the desktop as new PDFs.
- Reorder, rotate, delete pages directly in the sidebar.
- Sign: capture a signature with the trackpad or camera once, reuse it forever.
- Mark up: the full annotation toolbar — shapes, text, highlights, freehand.
- Reduce size: Export with the Reduce File Size Quartz filter.
One caution on that last item: the built-in Reduce File Size filter is aggressive and can visibly degrade images. For anything where quality matters, a compressor with an adjustable level is the better choice — Compress PDF runs in the browser and lets you see the trade before committing.
Which to use
| Need | Use |
|---|---|
| Reading and light markup | The built-in viewer or a browser |
| Merging and splitting | Preview on macOS, or a browser tool anywhere |
| Filling complex forms | Adobe Reader — XFA support is exclusive |
| Digital signature validation | Adobe Reader |
| Redaction and deep editing | Acrobat Pro or a dedicated editor |
| Sensitive documents | Anything that works locally |
The honest summary is that Adobe Reader is needed for two things — XFA forms, which some government and banking systems still use, and validating digital signatures — and not much else. Everything on the rest of that list has a good built-in or browser-based answer.
Frequently asked questions
How do I change the default PDF viewer on Windows?
Settings → Apps → Default apps, then search for .pdf and pick the application. Use this route rather than right-click → Open with, which is less durable and often reverts.
Why does Windows keep resetting my PDF association?
Usually Adobe Reader reclaiming it on update — turn off its default-handler prompt in preferences. Feature updates have also reset associations, and on a work machine it may be enforced by policy, in which case no local setting will hold.
How do I set the default PDF app on a Mac?
Select any PDF in Finder, press Cmd-I, change "Open with", then click Change All. Without Change All the setting applies only to that one file, which is why it often appears not to work.
How do I make Chrome open PDFs instead of downloading them?
Settings → Privacy and security → Site settings → Additional content settings → PDF documents, and choose Open PDFs in Chrome. Chrome can also be set as the system handler for PDF files on disk.
How do I combine PDFs on a Mac without extra software?
Open one in Preview, show the thumbnail sidebar with Cmd-Option-2, and drag another PDF file into the sidebar — its pages insert at the drop point. Drag to reorder, then save.
Do I still need Adobe Reader?
For two things: filling XFA forms, which some government and banking systems still use, and validating digital signatures. For reading, annotation, merging, splitting and compressing, built-in viewers and browser tools cover it.
Is Preview's Reduce File Size any good?
It works but is aggressive and can visibly degrade images, with no adjustment available. Use a compressor with a settable level when image quality matters.