I'm trying to convert a PDF to PDF/A. At every pass I'm getting the error "GPL Ghostscript 9.19: Annotation set to non-printing, not permitted in PDF/A, reverting to normal PDF output". 
The PDF has previously been generated from HTML by wkhtmltopdf. With the error being quite vague I've done some research around PDF annotations. I've confirmed the PDF has no annotations, flattening annotations (though there isn't one) hasn't worked, I tried the -dShowAnnots=false switch. All to no avail. I've also tried it with a variety of different PDFs and I'm getting the same error on them all. 
The command I'm using to do the conversion is "gs -dPDFA=2 -dNOOUTERSAVE -sProcessColorModel=DeviceRGB -sDEVICE=pdfwrite -o output.pdf /Users/work/Documents/Projects/pdf-generator-service-tests/PDFA_def.ps -dPDFACompatibilityPolicy=1 input.pdf"
I tried creating a basic PDF page from Google's homepage using wkhtmltopdf https://google.com putput.pdf and again, no joy (this is an example of the PDFs I've tried to convert, for people who may want to try and replicate the issue).