Error message - 'This file is a certified PDF and could not be split'

Hello

I am having some trouble understanding what to do about the following error message - 

'This file is a certified PDF and could not be split'

I coordinate training and am required to issue training certificates to learners however, before they can be issued I must have them signed by the specific trainers. I use the 'request e-signatures' tool to do this.
When the signed certs are returned to my Adobe account, I then need to split the document into individual files i.e., cetificates.
So, I download and save the signed certs in one file to my computer - open that file in Acrobat - select the 'split PDF' tool - choose the file I want to split - use the scissor tool to split - click continue... This is when I am confronted with the 'This file is a certified PDF and could not be split' error message. 

I understand from some troubleshooting literature I have read so far that, if I were to 'uncertify' the document/files then this would remove the signature - is this correct?

And, does anyone know a way around this issue... Basically, I want to be able to split the document into its individual files with the signature still intact. 

Any help would be much appreciated!
Thank you 🙂