Pandoc PDF Error Resolution

This skill provides a step-by-step workflow for diagnosing and resolving "unknown error" messages when using pandoc to generate PDFs.

When to Use

Use this skill when:

• Pandoc returns an "unknown error" during PDF conversion
• The conversion succeeds for other formats (e.g., markdown, HTML) but fails for PDF
• You need to identify which PDF engine is available and working

Step-by-Step Procedure

Step 1: Verify Pandoc Installation

First, confirm pandoc is installed and check its version:

pandoc --version

This confirms pandoc is available and shows the version number. Note that pandoc itself doesn't generate PDFs directly—it delegates to external PDF engines.

Step 2: Check Available PDF Engines

Identify which PDF engines are installed on the system:

which pdflatex xelatex lualatex wkhtmltopdf pdfroff 2>/dev/null || echo "Checking individual engines..."
which pdflatex
which xelatex
which lualatex
which wkhtmltopdf

Common engines and their characteristics:

• pdflatex: Fast, widely available, good for basic documents
• xelatex: Better Unicode/font support, recommended for complex documents
• lualatex: Advanced typography, Lua scripting support
• wkhtmltopdf: HTML-to-PDF conversion, good for web-style documents

Step 3: Attempt Conversion with Explicit Engine

Retry the conversion with an explicit --pdf-engine flag:

pandoc input.md -o output.pdf --pdf-engine=xelatex

Try engines in this order:

1. xelatex (best Unicode support)
2. pdflatex (most widely available)
3. lualatex (if xelatex fails)
4. wkhtmltopdf (for HTML-heavy content)

Step 4: Capture Full stderr Output

Always capture the complete error output before falling back:

pandoc input.md -o output.pdf --pdf-engine=xelatex 2>&1 | tee pandoc_error.log

This preserves the full error message for analysis. Common error patterns:

• Font errors: Missing LaTeX packages or fonts
• Package errors: Missing LaTeX packages (use tlmgr install <package>)
• Syntax errors: Issues in the source document

Step 5: Install Missing Dependencies (if needed)

If errors indicate missing LaTeX packages:

# For TeX Live
tlmgr install <package-name>

# For Debian/Ubuntu
apt-get install texlive-latex-extra texlive-fonts-recommended

# For macOS with Homebrew
brew install --cask mactex

Step 6: Fallback Strategies

If all engines fail, consider:

1. Convert to HTML first, then use wkhtmltopdf
2. Simplify the document (remove complex formatting)
3. Use an online conversion service
4. Generate PDF from a different format (e.g., DOCX via LibreOffice)

Example Complete Workflow

#!/bin/bash
# pandoc-pdf-debug.sh

INPUT_FILE="$1"
OUTPUT_FILE="${INPUT_FILE%.md}.pdf"

echo "=== Pandoc PDF Conversion Debug ==="
echo "Input: $INPUT_FILE"
echo "Output: $OUTPUT_FILE"

# Step 1: Verify pandoc
echo -e "\n[1] Checking pandoc version..."
pandoc --version | head -1

# Step 2: Check engines
echo -e "\n[2] Checking available PDF engines..."
for engine in pdflatex xelatex lualatex wkhtmltopdf; do
    if which "$engine" &>/dev/null; then
        echo "  ✓ $engine: $(which $engine)"
    else
        echo "  ✗ $engine: not found"
    fi
done

# Step 3: Try conversion with xelatex
echo -e "\n[3] Attempting conversion with xelatex..."
pandoc "$INPUT_FILE" -o "$OUTPUT_FILE" --pdf-engine=xelatex 2>&1 | tee /tmp/pandoc_error.log

if [ $? -eq 0 ]; then
    echo "✓ Conversion successful!"
else
    echo "✗ Conversion failed. Check /tmp/pandoc_error.log for details"
    echo "Attempting fallback with pdflatex..."
    pandoc "$INPUT_FILE" -o "$OUTPUT_FILE" --pdf-engine=pdflatex 2>&1
fi

Quick Reference

Command	Purpose
pandoc --version	Verify pandoc installation
which xelatex	Check if xelatex engine exists
pandoc file.md -o file.pdf --pdf-engine=xelatex	Convert with explicit engine
... 2>&1 | tee error.log	Capture full stderr output
tlmgr install <pkg>	Install missing LaTeX package