We apologize for the inconvinience caused, as per the description above, you are getting Adobe Application Manager missing or damaged and error message of Invalid serial number, Is that correct?
I have checked the records and found that you have a perpetual license of Acrobat Standard DC registered on your current Adobe ID.
Please use the Adobe Acrobat cleaner tool to remove the installed and leftover of Acrobat Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs Link: https://labs.adobe.com/downloads/acrobatcleaner.html
Restart the computer, and then install the Acrobat Standard DC from the following link Download Pro or Standard versions of Acrobat DC, 2017, XI, or X Link: https://helpx.adobe.com/in/acrobat/kb/acrobat-downloads.html
Then use the serial key for the activation.
Hope this helps, and let us know how it goes.
Thank you for your quick reply. After I posted my original message, I remembered that I purchased my laptop from Dell with the Acrobat already installed. So I called their tech support and they were able to reinstall my original program which is functioning great. Although I can't give you specifics, the technician said this was a bug in the Acrobat program and he needed to consult a few forums (maybe these) to find the solution. Thanks again.
Angela, that's so awesome to hear. that it's working now.
Give us a shout if you need any assistance with Acrobat/Reader in future.