Hi Rachels,
As per the issue description, you are receiving above mentioned error when trying to save pdf after using Fill & SIgn in Adobe Reader, is that correct?
Please try following troubleshooting steps:
1- Check for updates - click Check for Updates under Reader's help menu and see Reader is running the latest patch.
2- Try fill & sign option on another pdf file.
3- Launch Reader > click Edit > Preferences > under Security (Enhanced).
Uncheck the box next to Enable Protected Mode at startup > click OK > relaunch Reader and try again.
Please note: Disabling protected mode is for the troubleshooting purpose only. Please turn the feature back on when troubleshooting is complete.
4- If you also have Adobe Acrobat installed on the machine, you can print the pdf to Adobe PDF printer and see if that helps.
Open the pdf in Acrobat > click File > Print > under Printers > select Adobe PDF and click Print. (i would like to mention that Adobe PDF printer comes with Adobe Acrobat).
Could you please let us know the dot version of Reader installed on the machine :Identify the product and its version for Acrobat and Reader DC
Which operating system is installed on the machine- Mac/Windows?
Keep us posted with the results.
Shivam