TL;DR: "Unable to convert document" is the wrapper's generic message - Ghostscript's real error is on stderr. Re-run it with stderr visible to see the actual failure, and expect it to be the signature: signed PDFs use incremental updates that the PDF/A writer cannot faithfully rewrite. Convert an unsigned working copy instead, and keep the signed original as the legal record.

```text
unable to convert document
```

1. Re-run the conversion with stderr unhidden:
   `gs -dPDFA -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=out-a.pdf signed.pdf`
   Expected: stderr shows the real PostScript error (often around incremental updates or permissions).
2. Check whether the file is signed or encrypted:
   `qpdf --check signed.pdf`
   Expected: signature dictionaries or encryption flags - the usual blockers.
3. Render an unsigned working copy:
   `gs -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=working-copy.pdf signed.pdf`
   Expected: a visually identical PDF with the signature structures flattened away.
4. Run the PDF/A conversion on the working copy.
   Expected: conversion succeeds and a validator confirms PDF/A compliance.
5. Archive both: the signed original as the legal record, the PDF/A copy as the preservation copy, linked in your metadata.

## Use this when
- Ghostscript (or a tool wrapping it) fails PDF/A conversion only on signed contracts
- the error message is generic with no PostScript details
- unsigned contracts convert fine with the same command

## Not for this skill when
- Ghostscript is not installed or not found (fix the install first)
- the real stderr error is about missing fonts (embed the fonts instead)
- every PDF fails conversion (check the Ghostscript version and command syntax)

## Variant phrasings
### ghostscript pdf/a conversion signed pdf fails
### ghostscript unable to convert document pdfa
### convert signed pdf to pdf/a workaround

## Why it happens
Digital signatures live in incremental updates appended to the PDF. The pdfwrite device rebuilds the file from scratch for PDF/A, and it cannot preserve signature structures through that rewrite - so it fails (or the wrapper gives up and prints the generic message). The content is fine; the signature container is what breaks.

## Edge cases
- Never present the unsigned PDF/A copy as the signed original - the signature is gone.
- Missing-font errors look similar at first glance; always read stderr before assuming it is the signature.
- PDF/A-1 forbids transparency and layers that A-2 and A-3 allow - pick the right conformance level for the source.
- Some signers lock the file against any processing; the print-to-PDF path through a viewer is the fallback.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst__jyMVAU3XfwXlJgAbkAyoA