For each PDF/A-1 validation issue we try to explain what it means and, if possible how to resolve it. For a more technical explanation of the issue we quote the related section of the ISO 19005-1 PDF/A Specification.
Values other than "{/None}" are prohibited for the key <<SMask>> The key <<SMask>> is prohibited for PDF/A-1b The key <<Group>> is prohibited for PDF/A-1b Value "Multiply" is prohibited for the key <<BM>> Value "1" for the key <<CA>> is required Value "1" for the key <<ca>> is required
6.4 - ISO 19005-1 PDF/A Specification:
If an SMask key appears in an ExtGState or XObject dictionary, its value shall be None.
A Group object with an S key with a value of Transparency shall not be included in a form XObject.
The following keys, if present in an ExtGState object, shall have the values shown:
-- BM Normal or Compatible
-- CA 1.0
-- ca 1.0
NOTE: These provisions prohibit the use of transparency within a conforming file. The visual effect of partially transparent graphics can be achieved using techniques other than the use of the PDF Reference transparency keys, including pre-rendered data or flattened vector objects. The use of such techniques does not prevent a file from being PDF/A-1 conformant.