MS Word tasks stuck after closing when Acobat 2020 PDFmaker add-in is active

Hello Adobe community,

since a few days ago we try to troubleshoot an issue with Acrobat 2020 PDFmaker add-in in MS Word 2016.

Actual Behaviour:

The add-in is loaded and works correctly. However, when we close the last open MS Word 2016 window, you can still find at least one running Word task in Task manager. Tick „View“ → „Group by Type“ in Task Manager to see that it is moved from the „Apps“ section to the „Background Processes“ section of the process list. These „ghost tasks“ do not occur when we disable the Adobe PDFmaker add-in in MS Word options.

Expected behaviour:

Word processes should terminate completly when the last open Word window is closed. Why is this problematic? We have a third party application that is launching Word tasks, RPC'ing some stuff, saves the doc and waits for the processes to terminate – which happen never happens, so the system is stuck.

Steps to reproduce:

1. Open MS Word, activate the PDFmaker.dll add-in
2. Close MS Word, reboot
3. Open MS Word, write a line or not, do nothing
4. Close MS Word: The window is closed but task is stuck in the list of „background processes“

Here's the details:

• ☑ Problem occurred first on Dec 6, 2022 on several client machines. Machines are up-to-date Acrobat-/OS-/Office-wise, no relevant updates were installed in the days before.
• ☑ There's no virus scanner aside from MS Defender running on that system, but there's nothing in the System logs indicating any overblocking/ASR-matches
• ☑ We reinstalled Acrobat 2020 (MSI-Package)
• ☑ We searched this Forum, a post from 2018 with similar symptoms had no solution
• ☑ We checked the Acrobat FAQ
• ☑ We checked the List of Acrobat Known Issues
• ☑ We're positive that macros/no-macros and further add-ins can be ruled out. (There's two more active add-ins, one is for MS OneNote linked notes and one CRM export thingy. They don't interfere.)
• ☑ We started Word in safe-mode (press Ctrl during launch) without any add-ins – when closing, no ghost task is stuck

Environment:

• Microsoft Office Professional Plus 2016, version 16.0.4266.1001 (64-Bit) up-to-date
• Microsoft Windows 10 Enterprise 21H2 build 10.0.19044 (64-Bit) up-to-date
• Acrobat 2020 v20.005.30418, PDFmaker add-in dll-file version 20.5.30407.10407 (.../x64/PDFMOfficeAddin.dll, .../x64/PDFMWord.dll)
• Internet connection via HTTP proxy

Acrobat Debug Information:

(generated in German, but you'll get it anyways)

Acrobat-Details: 
   Sandboxing: Aus
   Geschützte Ansicht: Aus
   Captive Reader: Nein
   Unterstützung für mehrere Reader-Instanzen auf Desktop: Aus
Anzeigedetails: 
   Bildschirmbreite: 2560
   Bildschirmhöhe: 1440
   Anzahl der Monitoren: 2
   Anzahl der Maustasten: 5
   Mit Mausrad: Ja
   Mit Digitalstift: Nein
   Doppelbyte-Zeichensatz: Nein
   Mit Eingabemethoden-Editor: Ja
   In Bildschirmsprachausgabe: Nein
Benutzername: ...
Betriebssystemhersteller: Microsoft Corporation
Betriebssystemname: Microsoft Windows 10
Betriebssystemversion: 10.0.19044  
BIOS-Version: HPQOEM - 0
Gebietsschema: Deutsch (Deutschland)
Gesamter realer Speicher: 4194303 KB
Gesamter virtueller Speicher: 4194176 KB
Grafikkarte: Intel(R) UHD Graphics 620
    Version: 26.20.100.7324
    Test: Nicht unterstützt
Größe der Auslagerungsdatei: 4194303 KB
Installierte Acrobat-Version: C:\Program Files (x86)\Adobe\Acrobat 2020\Acrobat\Acrobat.exe
    Version: 20.5.30418.10418
    Erstellungsdatum: 2022/11/10
    Erstellungszeit: 09:14:28
Installierte Anwendungen: 
   Office-Version: Office 2016 64-bit
   Outlook-Version: Outlook 2016 64-bit
Kontodetail: 
   Benutzerrechte: Normal
   Benutzerkontensteuerung: Standard
   Prozessintegrität: Mittel
   Profiltyp: Keine
Monitor: 
    Name: Intel(R) UHD Graphics 620
    Auflösung: 2560 x 1440 x 59
    Bit pro Pixel: 32
Prozessor: Intel64 Family 6 Model 142 Stepping 12  GenuineIntel  ~1800  Mhz
Sitzungsdetail: 
   Boot-Typ: Normal
   Wird heruntergefahren: Nein
   Netzwerk: Verfügbar
   In Citrix: Nein
   In VMWare: Nein
   Remotesitzung: Nein
   Fernsteuerung: Nein
   Verwenden von JAWS: Nein
   ZoomText verwenden: Nein
   Verwenden von Windows-Eyes: Nein
   Verwenden von NVDA: Nein
Standard-Browser: 
Standard-E-Mail-Anwendung: Microsoft Outlook
    mapi32.dll
    Version: 1.0.2536.0 (WinBuild.160101.0800)
    Erstellungsdatum: 2022/11/09
    Erstellungszeit: 10:57:48
Systemname: B010-W-CLTNO98
Temporärer Ordner: C:\Users\...\AppData\Local\Temp\
Verfügbarer realer Speicher: 909872 KB
Verfügbarer virtueller Speicher: 3874128 KB
Windows-Details: 
   Tablet-PC: Nein
   Starter Edition: Nein
   Media Center Edition: Nein
   Langsamer Rechner: Nein
Windows-Verzeichnis: C:\WINDOWS
Zeitzone: Mitteleuropäische Zeit

Any ideas? Do you need any more information? Is there any PDFmaker-specific log files to check? Is there any logs/details for MS Word?

Regards