[Reader][Win7] 21208 update breaks Acrobat Reader, won't start, missing dll

Update - March 8

BTC got a chicken bone in his throat this afternoon.  After making the registry change that he found (but has not yet posted) Adobe opened for several days consistently without the hateful AdobeCollabSync.exe  error message pop-up.

But today, it has begun again (yes, the registry change is still there).  So BTC has implemented the easier change which is to simply disable (by renaming)  two Adobe system files that “activate” the Adobe Collaborative System.  This was recommended by users on on other Adobe sites.

The two files are AdobeCollabSync.exe and FullTrustNotifier.exe (be certain that Windows Explorer is set to "show file-name extensions”).  For the 32-bit Version 25.001.21265, start in Drive C:\ and follow the path (the folder names are those shown on Bobthecat's computer - your may vary slightle):

            Drive C:\ ProgramFiles(x86)\Adobe\AcrobatReaderDC\Reader     [be certain to use (x86)]

Within the \Reader folder, scroll down to find files:  AdobeCollabSync.exe                                                                                                               FullTrustNotifier.exe

Change the file names to something like:                  AdobeCollabSyncOLD.exe                                                                                                         FullTrustNotifierOLD.exe

This disables the files because Adobe won't find the files it is expecting.  Adding "OLD" at the end of the file name will keep these files in the original positions in the \Reader folder, so that if a later Adobe updated puts in new versions they will be easy to spot.  By not simply deleting the two original files, you can undo the change by restoring them to their original names.         

BTC will keep you posted.  

I uninstalled Version:  25.001.21265 because it had TWO errors!

I then installed version: AcroRdrDC2500121223_en_US and now this version will NOT open and has the same damn error: api-ms-win-core-winrt-I1-1-0.dll is missing from your computer

So WTF do I do now?

People keep saying download the patch but WHICH one exactly?
All of the links have multiple rows of patches!

Can someone PLEASE answer me and include a link to the correct patch?

Thanks!!!

Update #2 - 6 Mar:   At the risk of being overly optimistic, Bobthecat (after a lot of catnip) thinks he has found the solution for the intrusive popup he posted earlier.  The key is “AdobeCollabSync.exe” in the header.  Paraphrasing a Google search result:   “AdobeCollabSync (Adobe Collaboration Synchronizer) is an Adobe background process that synchronizes shared PDF reviews, cloud documents, and comments across Adobe apps like Acrobat and Creative Cloud.  It acts as a bridge for cloud-based collaboration features, allowing real-time syncing of documents.  It often causes performance issues, such as high CPU usage and locked files, where PDFs cannot be edited or moved (see Adobe’s community forum).  IT IS NOT ESSENTIAL FOR USING ADOBE READER FOR BASIC PDF VIEWING AND PRINTING”  (italicized emphases by Bobthecat).

There are two methods that seem to be the most recommended for disabling AdobeCollabSync.  1)  Disabling two files (deleting or renaming - BTC prefers renaming since it can easily be un-done),  2)  making a single entry in the registry (this is daunting for users not familiar with mucking in the registry).  BTC has done Method 2 (registry entry), because it might be less affected by program updates that Method 1.  IT HAS SEEMED TO WORK SO FAR - but BTC has had to eat those words (without the benefit of catnip) to meow loudly just yet.  He has not tried Method 1, but it seems easy to do and has been said to work without having to get into the registry (intimidating and risky).  Doing both methods are the “belt and suspenders” approach. BUT, there is a strong possibility that Method 1 and maybe Method 2 might be overwritten the next time Adobe pushes down another involuntary update. 

Your BTCat will try to post both Methods (with detailed instructions) tomorrow, 7 Mar, if the solution still works as it does today.

Update 6 Mar:    In yesterday’s post I described updating two computers to Version 21265.  This morning, on both computers, Adobe Reader is not working properly when opening a pdf with Adobe -  gives error message:

Hitting OK three times makes message go away.  Reader seems to work, but there is no way of knowing what components are not working.   Once message goes away, it appears possible to close pdf, and re-open it (or new ones) without message occurring.  However, restarting (turn off then on computer) causes message to occur again on FIRST pdf opened.  Very annoying, and disconcerting to not know what is NOT working.

Adobe - PLEASE FIX.

New update post:  3/5/2026  1630

Yesterday I updated Reader to 2025.001.21265 on Computer One (Dell M2800, Win 7 Pro) which also has loaded on it SumatraPDF, FoxitPDF and Firefox (please remember these).  

A quick summary of the steps on Computer One is:  1)  put missing api..dll’s in appropriate System folders (as per HelpfulJohn).  2)  Downloaded and installed 2025.001.21223  3)  Use Adobe to open pdf.  Open correctly.  4)  After a while Adobe updated itself to 2025.001.21265.  5) disabled api….dll’s (changed names) in Systems files - Reader still worked.

Adobe behaved correctly:   1)  No “missing api...dll” message   2) No (not one) error message about WinHttpWebSocketCompleteUpgrade missing from dynamic link library WINHTTP.dll   3)  Using “Open With” to open a pdf, all four PDF readers listed above were shown as available, and they were all in the Windows Default Programs list for selecting default program to open pdf files.

Everything seemed to work as it should for Computer One.

---------------------------------

Today I updated Reader to 2025.001.21265 on Computer Two (Dell E6520, Win 7 Pro) - different story:

To do this update I removed Reader Version 22.003.20282, earlier suggested by one participant as working on Windows 7.  It had only kinda-worked for me (several issues).  You may have some other older version  installed - it doesn’t matter.

Steps:  1)  Downloaded 21223 install file from site given by Helpful John.  2)  Downloaded Acrobat Cleaner tool from https://www.adobe.com/devnet-docs/acrobatetk/tools/Labs/cleaner.html.  3)  Used Windows Programs and Features to uninstall older Reader (DO THIS FIRST), then Cleaner tool to remove all traces of old installation.  4)  Put each api….dll into appropriate System folder.    5)  Re-boot computer [precaution only].  6)  Install 21223 from executable . 7)  Download from https://www.adobe.com/devnet-docs/acrobatetk/tools/ReleaseNotesDC/continuous/dccontinuousmar2026.html#dccontinuousmartwentytwentysix   the 32-bit update file AcroRdrDCUpd2500121265.msp.   I believe (but am not sure) that this file will only update 2025.001.21223.  Click to install.  You should now have a “working” Version 21265.

BUT…. for Computer Two:  1)  when I opened a pdf using the 21265 updated file, I still got the error message about WinHttpWebSocketCompleteUpgrade missing from dynamic link library WINHTTP.dll .  Clicked OK three times to make it go away.  It kept coming back at random times  2)  SumatraPDR and Foxit no longer appeared in the “Open With” option list, nor did they appear in the Default Programs list for pdf files.  I had to uninstall/install SumatraPDF to get it back in the list.  On another computer with updated 21265 Adobe, Sumatra and Firefox pdf options (but not Foxit), Sumatra and Firefox went away from the lists. 

IMHO Adobe has not fully fixed the 32-bit Reader (still get the  WinHttp..Upgrade...HINHTTP.dll error message - randomly, on some of my computers but apparently not on others - and the disruption of “Open With” options).  I have no confidence in Adobe Reader despite Adobe’s effort to fix it.  For now I will use SumatraPDF.  It does not all the fancy features of Adobe, but it seems to correctly open, read and print the pdf files I tested it with.  And...it uses a fraction of the computer resources that Adobe uses.  Firefox has a problem printing pdf files which look correct on the screen but do not properly fit the page when printed.  I reported this to Mozilla a couple of days ago, and from the response I got they are looking at it.  We’ll see.

I hope my experience is of some help.  I want to thank HelpfulJohn for the effort he has put into this issue.

How do I fix Acrobat Reader error on Win 7: “api-ms-win-core-winrt-I1-1-0.dll is missing from your computer” in detail?
Everyone keeps saying open Reader and check for updates but it will NOT OPEN because of the missing .dll!

Can anyone please give a detailed answer on what to do?

Do I uninstall Reader or not?

Please post the link to install the update and name the update please because there are four of them in the list.

Thank you if anyone will take the time to post a detailed reply.

Hola AnandSri:  resulta que cuando empezaron todos los problemas, desinstalé el programa para poder comenzar todo desde el principio correctamente con la actualización.

He estado esperando respuesta para que se lanzara la actualización que indicas y por tanto ahora no puedo entrar a instalar la actualización, porque resulta que cuando intento instalar el programa Adobe Acrobat reader, sale un mensaje de error (W64 bits): se interrumpe, “codigo de error 150201” con lo que si no puedo instalar el programa, no puedo descargar la actualización y no puedo utilizar.

¿podrías ayudarme por favor?

Muy agradecido

I had a similar experience to that just described by HelpfulJohn.  Yesterday (3/3), on my “test” computer with the api...dll’s installed in the System folders, I opened Version 25.001.21223.  It seemed to work, and I did not get the error message described by Antoniusll which I had gotten earlier in the day.  After a few minutes, an “Update” pop-up box appeared.  I accepted.  The box stayed, and stayed and stayed - never closed, or said “update completed.”  I eventually closed Adobe, and re-opened it.  It now said Version 25.001.21265.  I closed it, disabled the api...dll’s , and re-opened.  It worked.  To my happy surprise, it was still working this morning in multiple teste.  I have not YET gotten the error described by Antoniiusll.

But, as noted by a couple of participants, unless you can open 25.001.21223 (which requires api….dll placed in the C:\Windows\SysWOW64 folder), it won’t auto-update.  Catch-22.

There is another (manual) update method described by AnandSri.  I have not tried this method.  Go to:  

 https://www.adobe.com/devnet-docs/acrobatetk/tools/ReleaseNotesDC/continuous/dccontinuousmar2026.html#dccontinuousmartwentytwentysix

There you will find several .msp files.  For those not familiar with .msp files (and I was not until now) these are Microsoft Installer Patch files.  They are supposed to work like .exe files (click to execute), but will only update already-installed files.  The one which seemed most appropriate to update 32-bit Version 25.001.21223 is AcroRdrDCUpd2500121265.msp. 

I have three “work” Win 7 computers to “fix”.  All have broken Version 225.001.21223 without the api...dll files added to the System folders. I may try the .msp update method on one.  If it works, I’ll do the same on the others.  If not, I’ll put the api...dll files in the system folders as a temporary solution, and hope that the auto-update works.

04/03/26 15:55

The instructions provided by Adobe Community Managers are not clear.

For those of you who are still having Acrobat problems this may help you.

In order to successfully install the latest version 25.001.21265 you may need to install the older version 25.001.21223 first. And to get that working download the missing dll file it needs.

You should then be able to start Acrobat, and then manually perform an update to get version 25.001.21265.

I have just done this myself and it worked for me.

This is what I did over the past few days.

1. Uninstall version 25.001.21223 and then re-install it again.

If you already have version 25.001.21223, then just go to step 3.

2. Install version 25.001.21223 from here:

https://get.adobe.com/reader/enterprise

Select Windows 7 and English (UK)

There is only one version

Reader 2025.001.21223 English UK for Windows (32 bit)

I have not used the other installing website links mentioned by Community Managers.

3. To get the missing dll file follow these steps:

4. Go to this website

https://www.dllme.com/dll/files/api-ms-win-core-winrt-l1-1-0

5. Scroll down and click on the large DOWNLOAD (in pink)

(Ignore any of the Ads that appear – don’t click on them)

(Ignore anything that says ‘Click to Continue’ – these are ads)

6. Acrobat Reader is 32 bit, so you only need to download the 32 bit one

7. Get the 32 bit version

Many different versions of the file are shown (most have same version number)

Scroll down and locate the x86 - 32 Bit one (the first one for version 10.0.9904.0 will do,

OR BETTER STILL the one which states this is middle column:

SHA256: 4fb6b6b759a6d9184b8d032bad76516ca8539c6102de02bc1e8de568bb

)

Click on DETAILS (in pink), and then START DOWNLOAD (in pink)

8. This file will be in your explorer downloads folder

api-ms-win-core-winrt-l1-1-0_x86

It’s a zipped file so double click on it and explorer will unzip it

9. On a pc that is 64 bit cpu:

You WILL have folder SysWOW64

Copy the file shown api-ms-win-core-winrt-l1-1-0.dll

to C:\Windows\SysWOW64

10. On a pc that is 32 bit cpu:

You will NOT have folder SysWOW64

Copy the file shown api-ms-win-core-winrt-l1-1-0.dll

to C:\Windows\System32

11. Once file has been copied, just start Acrobat Reader. No need to restart first.

12. Start Acrobat and update to latest version 25.001.21265 by doing this:

At top left select

Menu > Help > Check for Updates

It will show ‘Update is available’ and ‘Updating Adobe Acrobat Reader (25.001.21223)’, which is the version currently installed.

Click on ‘Download and Install’ which will take a few minutes.

It will probably tell you to ‘Close programs in use’. So just shut down Acrobat that is running, and then click ‘Retry’.

Hopefully it will successfully install version 25.001.21265

Just start Acrobat. I did not need to restart my pc.

Hello,

No matter what do (I’ve tried all those fixes mentioned below), I’m still getting
the application was unable to start correctly 0xc00007b
This has been a frustrating experience over the past two weeks.

Dirk