PDF/A Warning

This isn’t an error, but rather a warning. You’re getting it because you selected the "PDF/A-1b" option when you scanned.

PDF/A stands for "Archival-quality PDF". It’s a special type of PDF which is supposed to be readable for at least 30 years. To make that possible, the PDF/A format dictates that only a certain subset of the regular PDF features are allowed.

This message is warning you that making any changes to the PDF could jeopardize its status as a PDF/A.

If you find the message annoying, you can select the option to not show it any more.