Requirement: Flattened without any comments or layers, and pdf/a compliant. Bookmarks maintained

Hi,

I struggle with flattening, saving as pdf/a AND maintaining bookmarks.

I am working with documentation for oil and gas.

I now have to submitt the pdfs according to these requirement;

"Flattened without any comments or layers and pdf/a compliant. Bookmarks maintained."

I use Adobe Acrobat Pro DC 2015 Release (Classic), with Windows 11 Pro.

My pdf is a compiled file, with documents from different sources. Some parts are scanned certificates (I run OCR on these), some are datasheets in pdf from various suppliers and some are created from word. The frontpage and chapter pages are created in word. (And no, I can't get the suppliers of all these various documents to change the way they supply their file)

I have been searching and trying a lot of different descriptions, but I can't get mye files to comply to these requirements with the use of Adobe Pro DC.

I have tried to save to pdf/x, but get error message that it was not possible. I ran Analyze and fix like the error message said, but that did not come up with any errors to fix.

I have tried various descriptions using preflight, but have not had any sucess. 

HELP !!! 🙂 

Best regards

Irene