Acrobat DC 2015 error "Cos document table full"

You have 23 digital signatures? This is a disaster waiting to happen, it was never designed to work. This sometimes happens if people make the mistake of signing each page. 

Hi,

Can you be more specific on the steps that you've followed when you mention that you've tried all normal steps?

Also, by trying to split, merge, separate, or alter a digitally signed PDF is basically defeating the purpose of security. I am pretty sure that is probably why you're getting such error.

My suggestion, is to either Print to PDF, or  Save As Postscript file (also known as refrying a PDF), then split or separate.

However, refrying a PDF is strongly discouraged, for many reasons, and as a flattened output file, you will not be able to validate those signatures.

You can also try to go to Edit, Preferences, --->>> Signatures.

In the Digital Signatures preferences settings, see the "Verification" section, and click on the "More" button.

It will open the Signature Verification Preferences. You may change a few things here, where it says "Verification Behavior", and see specifically the "Windows Integration" section.

Now, I'm not sure if modifying any of these preferences would have anything to do with your initial question, but you can try and see.

Last, the best answer I can think off is through this Adobe guidance: https://helpx.adobe.com/sign/kb/split-up-a-signed-document.html