Hi alistairg39330077,
Thank you for reaching out, and sorry about the trouble caused.
As mentioned, you get the error when using the image option to add a signature. Please let us know if the error appears even when you try to use a different image file than the one you are trying to add. If you have not already checked, please check and confirm. If the new image is added without any issues, that means there is an issue with the previous image file.
Please share a screenshot of the error message you received. Also, let us know if you use the Acrobat desktop application to add the signature or Acrobat Sign.
Let us know if you need any help.
Thanks,
Meenakshi
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