Hope you are doing well and sorry for the trouble. As described when you edit a pdf on Adobe Acrobat Pro, the number 1 is replaced by /
Is this a behavior with a particular PDF file or with all the PDFs you try to edit ?
Would you mind sharing the version of the Adobe Acrobat Pro you are using? To check the version go to Help About Acrobat and make sure you have the latest version installed. Go to Help > Check for Updates and reboot the computer once.