The preview pane does not open your PDF in Acrobat. Windows passes the file to a small separate component called a preview handler, which draws a picture of the first page into the pane. That component can fail on its own while the reader beside it works.
So the first question is not what is wrong with the file. It is which preview stopped: File Explorer, Outlook, or Quick Look on a Mac. They use different machinery and they break for different reasons.
It is one of the more misleading faults on Windows, because everything you would normally check comes back clean. The file opens. The reader is installed. Other file types preview without complaint. Nothing about the symptom points at the part that actually failed, which is a piece of plumbing most people have never heard of.
The preview pane is not your PDF reader
When you click a file in Explorer with the preview pane open, Windows does not launch the associated program. It looks up a registered preview handler for that file type, starts it inside a host process, and asks it to render into the pane. Microsoft documents the mechanism for developers under preview handlers and the shell preview host, and the important part for anyone troubleshooting is the isolation: the handler runs separately, and it fails separately.
That separation cuts both ways. It means a broken preview tells you nothing about the file, and it means fixing the reader does not necessarily fix the preview. The two are related only by the fact that the same installer usually puts both on your machine.
Work out which preview stopped
Before changing anything, establish the scope. It takes under a minute and it decides which of the sections below applies to you.
Try a different file type
Click a Word document or a JPEG with the preview pane open. If those preview and PDFs do not, the problem is the PDF handler specifically. If nothing previews, the pane itself is off or the shell is at fault.
Try the same PDF in both places
Preview it in File Explorer and as an Outlook attachment. Working in one and not the other points at Outlook's own trusted list rather than at the handler.
Try a PDF you made yourself
Print any page to PDF and preview that. If a freshly made file previews and a particular document does not, the fault is in that document, not the machinery.
Windows: four fixes, in order
Work down the list. Each is quicker than the one after it and each resolves a different cause.
- Confirm the pane is actually on. In File Explorer choose View and then Preview pane, or press Alt and P. Windows 11 moved this into the View menu under Show, and a feature update occasionally turns it back off.
- Turn the handler back on in your reader. Acrobat and Reader both carry a setting for it, under Preferences and then General, described as enabling PDF thumbnail previews or showing previews in Explorer. If a competing reader was installed later, it may have taken the registration and then removed it on uninstall.
- Repair the installation. From Acrobat's Help menu, choose Repair Installation. This rewrites the registry entries that name the handler, which is exactly what a half-finished update tends to break.
- Check the architecture. A 32-bit preview handler cannot load inside 64-bit Explorer. Current Acrobat ships a 64-bit handler and this is no longer common, but on a machine running an older release it remains the likeliest cause and the fix is to move to a current version.
Outlook keeps its own list
Outlook uses the same handlers but runs them inside its own process and maintains a separate register of the ones it is willing to trust. A handler that works in Explorer can be switched off in Outlook and nowhere else.
The setting lives under File, then Options, then Trust Center, then Trust Center Settings, then Attachment Handling, where a button marked Attachment and Document Previewers lists every previewer with a checkbox. If the PDF entry is unticked, tick it. If it is missing entirely, the handler is not registered at machine level and the Windows section above is where to start.
Outlook also refuses to preview attachments it considers unsafe, and messages that arrived with a warning banner will show an error instead of a preview regardless of how healthy the handler is. Saving the attachment to disk and previewing it in Explorer distinguishes the two cases immediately.
macOS: Quick Look and its cache
On a Mac, pressing Space on a selected file calls Quick Look, which renders PDFs through the same system framework that Preview uses. It rarely breaks outright. What it does do is keep a cache of rendered previews, and a stale entry in that cache shows as a blank panel or a spinning indicator that never resolves.
Resetting the cache is a single command in Terminal, qlmanage -r cache, followed by pressing Space on the file again. If a particular document still refuses after that, and it opens normally in Preview, the file is using something the Quick Look renderer declines to draw, most often an unusual encryption setting or a damaged embedded font.
When the file is the problem after all
Occasionally the machinery is fine and one document genuinely will not render. Three characteristics account for nearly all of them.
A standard PDF under a few hundred pages.
Text, images and vector artwork.
No encryption, or a password you have already supplied.
Stored locally rather than as a cloud placeholder.
Password-protected files, which no preview handler will decrypt.
Very large documents, where the handler times out before the first page is drawn.
Files still syncing, where OneDrive or Dropbox holds a placeholder rather than the bytes.
Damaged files, which fail in the pane the same way they fail everywhere else.
The cloud placeholder case is worth knowing because it looks exactly like a handler fault. A file marked as online-only has no content on the machine until something asks for it, and a preview request does not always trigger the download. Opening the file once, which does trigger it, makes the preview work from then on.
If the document turns out to be genuinely damaged, the preview is the least of it, and rebuilding the file is the real fix.
Repair a damaged PDF
Structure rebuilt where that is possible, pages re-rendered where it is not. Nothing uploaded.
Common questions
What the preview pane is, and what to do when it stops.
01Why does my PDF open fine but not preview?
Because the preview pane does not use your PDF reader. Windows hands the file to a separate component called a preview handler, and that component can be missing, unregistered or the wrong architecture while the reader itself is perfectly healthy.
02How do I turn the preview pane on in Windows?
In File Explorer, open the View menu and choose Preview pane, or press Alt and P. If the pane appears but stays empty for PDFs specifically, the handler rather than the pane is the problem.
03Why does Outlook show a preview error for PDF attachments?
Outlook uses the same preview handlers as Explorer but runs them inside its own process, and it keeps a separate list of handlers it trusts. Turning the PDF handler back on under Attachment and Document Previewers usually restores it.
04Does the 64-bit version of Acrobat matter?
It used to matter a great deal. A 32-bit preview handler cannot run inside 64-bit Explorer, and for years that mismatch was the single most common cause. Current Acrobat installs a 64-bit handler, so this mainly affects older versions.
05Why did previews stop after a Windows update?
Updates and repairs can reset the registry entry pointing at the handler, and some feature updates clear the trusted list in Outlook. Reinstalling or repairing the reader rewrites the entry.
06My Mac stopped showing PDFs in Quick Look. What now?
Quick Look keeps a cache that can go stale. Resetting it with qlmanage in Terminal, then pressing Space on the file again, resolves most cases without touching any application.