Three independent switches decide whether Explorer draws a first page or a generic icon, and they live in three different dialogs. Check them in this order: Folder Options, then Performance Options, then your reader's own setting.
If all three are right and thumbnails still fail, clear the thumbnail cache. If they fail for some files and not others, it is the files, and the section on that below explains what they have in common.
The frustrating part is that the three controls do not know about each other. Turning the first one on while the second is off produces exactly the same result as leaving both off, so it is easy to believe you have fixed the setting and found it made no difference.
Thumbnails are not previews
It is worth separating the two before going further, because they are often confused and they are genuinely different systems. A thumbnail is a small static image of the first page, generated once by a component called a thumbnail provider and then stored in a cache so that browsing a folder stays fast. Microsoft documents the mechanism under thumbnail handlers.
The preview pane, by contrast, runs a live handler every time you select a file and draws into the panel at the side of the window. Different component, different registration, different cache. That is why one can be perfectly healthy while the other is not, and why an empty preview pane is a different problem with a different answer.
The three switches, in order
Folder Options: always show icons
In File Explorer, open the three-dot menu and choose Options, then the View tab. Near the top of the advanced list is Always show icons, never thumbnails. Clear it. This is the switch that is set wrongly most often, usually because somebody turned it on years ago to speed up an old machine.
Performance Options: show thumbnails
Press Windows and Pause, choose Advanced system settings, then Settings under Performance. On the Visual Effects tab, make sure Show thumbnails instead of icons is ticked. Choosing Adjust for best performance clears this box along with everything else, which catches a lot of people.
Your reader's own option
Acrobat and Reader carry a setting under Preferences and then General for enabling PDF thumbnail previews in Windows Explorer. Other readers have an equivalent. If this is off, the two Windows settings above will not help, because there is nothing registered to draw the page.
Clearing the cache
Windows stores generated thumbnails in a set of database files so that reopening a folder does not mean redrawing every page. Like any cache, it can end up holding something wrong: a blank entry written while a file was still copying, or a stale image from before the document was replaced.
The symptom that points here is specific. Thumbnails used to work, they stopped, and the files themselves have not changed. Run Disk Cleanup, tick Thumbnails, let it finish, and browse the folder again. Explorer regenerates what it needs as you go, so the first visit to a large folder is slower than usual and every visit after that is normal.
Clearing the cache is safe. Nothing in it is original data; every entry can be redrawn from the files themselves.
When only some PDFs show a thumbnail
This is a different problem from the settings above, and a more informative one. If most files in a folder show their first page and a handful do not, the settings are clearly right and those particular files have something in common. In practice it is one of four things.
- They are encrypted. A thumbnail provider will not prompt for a password, so a protected file gets the generic icon. This is deliberate, and it is a reasonable line for the shell to draw.
- They are cloud placeholders. A file marked online-only in OneDrive, Dropbox or iCloud Drive has no content on the machine until something requests it, and generating a thumbnail does not always count as a request. Opening the file once makes the thumbnail appear afterwards.
- They are damaged. A file whose first page cannot be rendered has no thumbnail to offer. If the same files also refuse to open, that is the real problem and the icon is a side effect.
- They came from a different generator. A very small number of PDFs use constructs the provider does not implement. These open fine everywhere and simply never acquire an icon, which is annoying rather than serious.
The architecture problem, and why it lingered
For a long stretch the single most common cause of missing PDF thumbnails was a mismatch nobody could see. Explorer runs as a 64-bit process on a 64-bit Windows, and a 32-bit thumbnail provider cannot be loaded into it. Acrobat shipped a 32-bit build as its mainstream product for years, so a correctly installed, fully working reader would provide no thumbnails at all.
Current versions install a 64-bit provider and the problem has largely gone, but it survives on machines running an older release, and it explains why so much advice written a few years ago recommends third-party shell extensions. On a current Windows with a current reader, none of that is needed. If you are on an older Acrobat and nothing else in this article has helped, updating it is the fix.
See every page, not just the first
Open a document and work with all of its pages as thumbnails you can reorder, rotate and delete. Runs in your browser.
Common questions
Why folders show icons instead of first pages, and how to get them back.
01Why do all my PDFs show the same icon?
Windows is drawing the file type rather than the file. Three separate settings can cause that: the Folder Options preference for icons over thumbnails, the performance setting that disables thumbnails system wide, and your PDF reader's own thumbnail option.
02Where is the setting to show thumbnails instead of icons?
In File Explorer, open Options, then the View tab, and clear the box marked Always show icons, never thumbnails. A second, separate control lives in Performance Options under Visual Effects.
03Why do only some PDFs show thumbnails?
Almost always because the rest are encrypted, still syncing as cloud placeholders, or damaged. A thumbnail provider will not decrypt a file, and it cannot draw a page whose bytes are not on the machine yet.
04How do I clear the Windows thumbnail cache?
Run Disk Cleanup, tick Thumbnails, and let it complete. Explorer rebuilds the cache as you browse. This fixes the case where thumbnails were working and suddenly stopped for files that have not changed.
05Are thumbnails and the preview pane the same thing?
No. They are separate components with separate registrations. Thumbnails are static images stored in a cache, while the preview pane runs a live handler each time you select a file, so one can work while the other does not.
06Does a non-Adobe PDF reader provide thumbnails?
Most do, and installing one takes over the registration. Uninstalling it can leave the slot empty rather than handing it back, which is why thumbnails often disappear after trying a different reader.