EPUB Skill

When to use

EPUB → PDF

• Convert EPUB books, papers, or distributed documents to PDF for reading and analysis
• Preserve layout and formatting before text extraction via pdftoppm
• Archive EPUB content in a fixed-layout format
• Prepare EPUBs for downstream processing (rendering, analysis, synthesis)

PDF → EPUB

• Convert papers and PDFs to reflowable EPUB format for ereader distribution
• Compress PDFs into smaller, device-friendly EPUB archives
• Auto-detect chapters and structure for better reading experience
• Redistribute research materials in open formats

Workflow

EPUB → PDF (for analysis)

1. Check for calibre → install if missing (brew install calibre)
2. Convert EPUB → PDF using ebook-convert with formatting options
3. Validate output → confirm PDF rendered correctly
4. Render pages → use pdftoppm to extract visual content
5. Analyze → pass to PDF skill for text extraction and synthesis

PDF → EPUB (for distribution)

1. Check for calibre → install if missing
2. Convert PDF → EPUB using ebook-convert with reflowable settings
3. Auto-detect chapters → ebook-convert scans for structure
4. Validate compression → confirm EPUB is smaller than PDF
5. Archive → save EPUB to research/sources/ for distribution or ereader use

Usage

EPUB → PDF (basic)

ebook-convert input.epub output.pdf

EPUB → PDF (with layout preservation options)

ebook-convert input.epub output.pdf \
  --pdf-standard-font "sans" \
  --paper-size "a4" \
  --margin-left 20 \
  --margin-right 20 \
  --margin-top 20 \
  --margin-bottom 20 \
  --pdf-mono-family "mono"

Note: Valid font families are: serif, sans, mono (not Helvetica, etc.)

PDF → EPUB (basic)

ebook-convert input.pdf output.epub

PDF → EPUB (with compression)

ebook-convert input.pdf output.epub \
  --output-profile "tablet" \
  --paper-size "a4"

Note: ebook-convert auto-detects chapters from PDFs. Inspect the output EPUB to verify structure.

In context (Sage workflow)

EPUB → PDF

# Convert EPUB to PDF for analysis
ebook-convert "/path/to/input.epub" "/path/to/research/sources/output.pdf"

# Verify and check size
ls -lh "/path/to/research/sources/output.pdf"

# Render pages for visual inspection
pdftoppm -png "/path/to/research/sources/output.pdf" "/tmp/preview/page"

PDF → EPUB

# Convert PDF to EPUB for distribution
ebook-convert "/path/to/input.pdf" "/path/to/research/sources/output.epub"

# Verify compression
ls -lh "/path/to/input.pdf" "/path/to/research/sources/output.epub"

# (EPUB will typically be 30-50% of PDF size)

Dependencies

System package:

# macOS (Homebrew)
brew install calibre

# Ubuntu/Debian
sudo apt-get install -y calibre

# Fedora/RHEL
sudo dnf install calibre

calibre includes ebook-convert and supports many formats:

• Input: EPUB, PDF, MOBI, AZW, AZW3, HTML, TXT, DOCX, ODT
• Output: EPUB, PDF, MOBI, AZW, AZW3, DOCX, HTML, TXT

Output conventions

• Location: Save files to research/sources/ with descriptive names
• Naming: Use title or slug: Author-Title.pdf, title-yyyy-mm-dd.epub
• EPUB→PDF: Check size (>100 KB typical for books)
• PDF→EPUB: Typically 30-50% of PDF size due to reflowable format
• Cleanup: Remove temporary files after verification

Quality checks

After EPUB → PDF:

1. File exists and readable
2. File size >100 KB (suspiciously small = text-only, may have lost images)
3. file output.pdf confirms it's a valid PDF
4. pdftoppm renders first page successfully

After PDF → EPUB:

1. File exists and readable
2. File size is 30-50% of original PDF (good compression ratio)
3. Unzip the EPUB and inspect content.opf for auto-detected chapters
4. Open in ereader or calibre viewer to verify reflowable layout

Troubleshooting

EPUB → PDF crashes or produces empty output

• Check if EPUB is corrupt: unzip -t input.epub
• Try without formatting options: ebook-convert input.epub output.pdf
• If EPUB has missing stylesheets (common), calibre will warn but continue
• Last resort: extract text from EPUB (unzip -p input.epub | grep -r "html") and convert to markdown

PDF → EPUB produces wrong chapter detection

• Run with --verbose to see what calibre detected: ebook-convert input.pdf output.epub --verbose
• For scanned PDFs (images), conversion may fail or produce text-only EPUB
• Use pdftotext first to extract text, then create EPUB from markdown

File size issues

• EPUB→PDF: if output is <50 KB, likely text-only (no images captured)
• PDF→EPUB: if output is >150% of input, likely includes images; use --output-profile "tablet" for better compression

Notes

• Layout preservation (EPUB→PDF): ebook-convert maintains structure, typography, images
• Reflowable format (PDF→EPUB): EPUB reflows to device width; fixed-layout PDFs may lose structure
• Chapter detection (PDF→EPUB): Automatic; works best on PDFs with clear page breaks or bookmarks
• Scanned PDFs: May fail or produce text-only output (no OCR)
• Large files: Some books convert to large files (100+ MB PDFs/EPUBs). Normal.

When conversion fails

• EPUB is corrupt: unzip -t input.epub (EPUBs are ZIP files)
• Verbose output: ebook-convert input.epub output.pdf --verbose for error details
• Unsupported format: Request original source in different format
• Manual fallback: Extract text from EPUB or PDF, save as markdown, document the failure

Related

• PDF Skill — for reading and rendering converted PDFs
• pdftotext — text extraction from PDF
• Calibre Handbook: https://manual.calibre-ebook.com/

Tested Conversions

✅ SHELLFISH.epub → SHELLFISH.pdf (73 KB → 639 KB, layout preserved, 89 pages)
✅ SHELLFISH.pdf → SHELLFISH-test.epub (639 KB → 262 KB, chapters auto-detected, 24 parts)

EPUB ↔ PDF bidirectional conversion pipeline ready. Last tested: 2026-04-29 | Calibre v5.x