Only app that I have found that has a documented way to produce pdf/a files with applescript is ABBY Finereader.
This script works with version 12 (the direct download version).
tell application "DEVONthink Pro"
set theSelection to the selection
repeat with theRecord in theSelection
set thepath to path of item 1 of theRecord
tell application "FineReader"
repeat until not (is busy)
end repeat
export to pdf thepath from file thepath export mode page image only make pdfa true
end tell
end repeat
end tell
This is pretty speedy and leaves the document untouched but for stripping out ocred text.
If you want the text then make the export line
export to pdf thepath from file thepath export mode text and pictures make pdfa true
This is just a variation of the script in this thread which shows the use of other parameters: ABBYY Finereader Pro v12
Its a conversion I would do only at the end before filing of the legal documents and only on duplicates.
Frederiko