I have a folder with about 20 Numbers files that I have created over the years. I have all the files marked to NOT show the extensions. Also have the Finder Preferences configured to NOT show extensions.

This morning almost all of the files show the .numbers extension. I have toggled the Finder Preferences to no affect. If I do a 'Get Info' on a file the hide extension box is checked but grayed out so I cannot access it.

Interestingly, if I duplicate the file, the duplicate does not show the extension and the high extension box is checked, as it should be, and accessible.

Have now discovered that all JPG files and some, but not all PDF files, have the extension showing and toggling the Finder Preference does not change this. So far word processing file do NOT have the extension showing.

Have deleted the Finder .plist logged out and logged back in with no change.

How do I fix this? Thanks in advance.

Have you run any updates lately...to either Numbers or your OS?

Have you rebooted your computer?

I'll go you one better and suggest a shut down/start up.

Since it's acknowledged that shutting down gets "deeper" into the OS than either logging out or restarting, it makes sense to skip the preliminaries and go straight to the main act.

Did a complete shut down and restart 15 minutes later. No change.

Have been using Sierra, OS 10.12.6, since it came out and updated Numbers about 6 weeks ago but extensions just started appearing in the past couple of days. Also JPG files and PDF files are showing the extension and no updates in those areas.

I wonder if you followed the correct procedure?

These posts by ganbustein inform about the hows and whys:

Bookmark shortcuts problem in Safari 8.0 | Networking | FineTunedMac

Can't mail audio files | Networking | FineTunedMac

I'm sorry to say I didn't understand any of your links.

I did however try this. I fired up my external HD with a clone of my system from March. Then I navigated to my internal HD Preference folder and deleted the Finder .plist. and rebooted.

No change. Numbers files still showing the extension.

You understood enough of ganbustein's posts to figure out an alternative approach, and if your Finder prefs reverted to factory default, what you did accomplished your purpose.

More: Actually, if you accomplished your purpose I think your extensions should be showing, because it's default, but I don't know if you can toggle them off, because my experience has been that toggling that Finder pref only affects newly created items.

I toggle Finder > Preferences > Advanced > Show all filename extensions on and off regularly and it effects every file regardless of when they were created*. The extensions are, always there, the only difference is whether or not Finder displays them.
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*Prior to OS X Apple used hidden parameter files instead of extensions to designate file type and what app they belonged to and if your files are from that era they may not have an extension. Such files would, of course, predate Numbers.

Sorry, I rechecked and found that I didn't describe my experience quite correctly: a file created under "Show" retains its extension if I toggle to "Don't show", but I can toggle a file created under "Don't show" repeatedly. (I haven't tried in every OS version, but I first ran into that behavior in Jaguar.)

More: It just occurred to me to experiment, and I found that the behavior I described pertains to my desktop, but not Finder windows.

OK, it looks like the pref is NOT applicable to items in ~, but, for instance, .tiffs toggle in /Users/artie/Pictures while .jpgs and .pngs don't.

Just so we are all on the same page…

1. The Finder .plist has only a single parameter about showing extensions and only two possible values Yes and No.
   • Deleting that property list and allowing it to be recreated should have cleared up any damage there
   • the default value is NO
   • in any case setting that value to YES (checking the box in Finder > Preferences > Advanced) would force all of the extensions on your system to show not just some of them.
2. If either Finder or Get Info is set to show the extension — the extension WILL show. (I just tested that out to satisfy my own curiosity.)

THEREFORE IF

• Finder > Preferences > Advanced > Show all filename extensions is UNchecked and…
• in Get Info in those files "Hide extension" IS checked and…
• any of the extensions are showing or…
• some but not all file extensions are showing…
• THEN it would appear likely the problem is in the OS itself.

For what it is worth, I learned long ago when working in tech support that a problem like that can take forever to troubleshoot and solve but it can almost always be "fixed" by reinstalling the OS which at best takes less than an hour and is dead simple to do. Just boot from the Recovery Drive and run the installer.

It it were me, while I was booted from the Recovery Drive, I would run Disk Utility > First Aid on the hard drive before reinstalling the OS, just to be sure there isn't an underlying problem there.

NOTE: Unless there are overriding reasons for staying permanantly with Sierra, this would be a good time to upgrade to High Sierra. (Even Artie finally gave in and upgraded )

Just to clarify exactly what is happening. Folder with 20+ Number files. Each file has been marked 'Hide Extension' in the Get Info panel. The numbers file extensions are still showing. Finder Advance Preference 'Show File Extensions' is Unchecked.

For years this folder has never shown the .numbers Extension. When I deleted the Finder .plist everything returned to default. Toggling the Finder Advance Preference has no affect.

Thanks for clarifying the default value of Show/Don't Show as "Don't Show".

To reiterate, though, a new item on my desktop created under "Don't Show" can be toggled while a similar item created under "Show" CANNOT be toggled...is stuck at "Show".

However, if I then check "Hide Extension" in Get Info the extension can thereafter be toggled until I uncheck it when it reverts to non-toggleable.

Clarification, please: "everything returned to default" means that the extensions disappeared?

When I deleted the Finder .plist, all of the Finder Preference setting returned to default. The 'show file extensions' box is UNCHECKED by default.

There was no change to the folder with the Numbers files, still shows the extensions even though the Finder Preference is Unchecked and the Get Info 'hide extension' IS checked.

That's what I was wondering.

Something, somewhere, is corrupted.

Reinstalling Sierra or upgrading to High Sierra do, indeed, sound like your best options.

I was initially hesitant to upgrade to High Sierra because I thought I would have trouble with a couple of 32 bit applications that I use a lot for which there is no upgrade.

BTW, I totally agree something is corrupt I just can't figure out what. I had a very similar, or possibly the same, issue with extensions showing when they shouldn't many many years ago and I can't recall how it was fixed for the life of me. Old age and memory are not compatible.

32 bit apps were originally scheduled to bite the dust in macOS 10.14 Mojave, but it now looks like it will support them and 10.15 will be the cutoff; the reprieve will be nice, but we'll have to face unpleasant reality at some point.

I've had absolutely no problems with 32 bit apps in High Sierra.

Have you tried rerunning the latest Sierra Combo...if macOS will allow you to do so?

Now that it's been established that your issue is rooted in something in your home folder you can try moving Numbers related items other than .plists to your desktop, one at a time, to see if you can zero in on its source. (I'd restart after each move although logging out/in will probably suffice.)

How do I go about identifying 'Numbers related' items?

I'm guessing that it is something other than Numbers, 3rd party, that is causing this issue. Numbers has been updated since this started and didn't affect this issue.

Is there some application where I can set a date range and have it search for anything installed within that date range?

Find Any File can identify files with "Numbers" in their names and find files that were created after a given date (but not within a date range).

The Numbers update you mentioned wouldn't affect your issue if it's rooted in a support file rather than in the app itself.

login as a different user (create one if necessary) and see if the problem persists in the other user account.

The problem was absent from a Test User Account. Unable to narrow it down from there.

I upgraded from Sierra to High Sierra and that solved the problem.