Thank you for posting your question in the Microsoft Q&A forum.
There're many limitations in my environment test, so I cannot conduct a full test for you. However, based on my research, there are some suggestions may try to resolve your issue:
-Ensure the Adobe Acrobat plugin is installed and enabled in your browser
Open Edge > … > Settings > Cookies and site permissions > Scroll down to PDF documents > turn on Always open PDF files externally.
-Ensure to activate Open Documents in Client Applications by Default in Site collection features.
And select the Open with the client application option in the Library settings
-Ensure you integrated the Adobe Acrobat plugin for SharePoint
Go to M365 admin center > Settings > Intergrated apps > + Get Apps > search Adobe Acrobat > select Adobe Acrobat for M365 > Get it now
Get it now again > Deploy > On the Apps to deploy page > Adobe Acrobat for M365 > Choose users or group receive the plugin > Follow the instructions > Finish deployment > Done
After integrating the Adobe Acrobat plugin with SharePoint, simply click the PDF file, and it will open directly in Adobe Acrobat.
The references are listed here:
Open PDFs in Adobe Acrobat Browser Plugin by Default - Microsoft Q&A
Issue Opening PDFs Directly in Adobe from SharePoint Site - Microsoft Q&A
I hope this helps! If you have any other questions, feel free to ask.
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