pdf-reading skill

PDF Processing Guide

Overview

This guide covers essential PDF reading operations using Python libraries and command-line tools. For advanced features (pypdfium2 rendering, pdfplumber table settings, OCR fallback, encrypted/corrupted PDF handling), see REFERENCE.md.

Reading & Inspecting PDFs

Before doing anything with a PDF, understand what you're working with.

Content inventory

Run a quick diagnostic first. For simple tasks ("summarize this document"), pdfinfo + pdffonts + a text sample may suffice. For anything involving figures, attachments, or extraction issues, run the full set:

# Always: page count, file size, PDF version, metadata
pdfinfo document.pdf

# Always: does a text layer exist? No fonts → scanned/raster → see "Scanned documents"
pdffonts document.pdf

# If fonts are present: sample the text layer
pdftotext -f 1 -l 1 document.pdf - | head -20

# If figures/charts may matter:
pdfimages -list document.pdf

# If the PDF might contain embedded files (reports, portfolios):
pdfdetach -list document.pdf

This tells you:

means the PDF is scanned or raster-only: pdftotext will return nothing, so skip straight to "Scanned documents" below. Fonts shown as not embedded ("emb: no") with custom encodings may produce wrong characters on extraction.

• Page count and size — how big is the job?
• Font status — are any fonts present? An empty pdffonts table

clean text, or is it garbled (broken encoding)?

• Text extractability — when fonts exist, does pdftotext return

(Note: vector-drawn charts from matplotlib/Excel won't appear — see "Extracting embedded images" below)

• Embedded raster images — are there photos or raster figures?

• Attachments — are there embedded spreadsheets, data files, etc.?

Text extraction

pypdf for basic text:

from pypdf import PdfReader

reader = PdfReader("document.pdf")
print(f"Pages: {len(reader.pages)}")

# Extract text
text = ""
for page in reader.pages:
    text += page.extract_text()

pdftotext preserving layout (better for multi-column docs):

# Layout mode preserves spatial positioning
pdftotext -layout document.pdf output.txt

# Specific page range
pdftotext -f 1 -l 5 document.pdf output.txt

pdfplumber for layout-aware extraction with positioning data:

import pdfplumber

with pdfplumber.open("document.pdf") as pdf:
    for page in pdf.pages:
        text = page.extract_text()
        print(text)

Visual inspection (rasterize pages)

Text extraction is blind to charts, diagrams, figures, equations, multi-column layout, and form structures. When any of these matter, rasterize the relevant page and Read the image:

# Rasterize a single page (page 3 here) at 150 DPI
pdftoppm -jpeg -r 150 -f 3 -l 3 document.pdf /tmp/page

# pdftoppm zero-pads the output filename based on TOTAL page count
# (e.g., page-03.jpg for a 50-page PDF, page-003.jpg for 200+ pages)
# Don't guess the filename — find it:
ls /tmp/page-*.jpg

Then Read the resulting image file. This gives you full visual understanding of that page — layout, charts, equations, everything.

When to rasterize vs. text-extract:

for data, image for context — this is what Claude's API does natively with PDF uploads)

• Content/data questions → text extraction (cheaper, searchable)
• Figures, charts, visual layout → rasterize the page
• Tables → try text extraction first, rasterize if garbled
• Precision matters → do both (extract text AND rasterize; use text

Token cost awareness:

• Text extraction: ~200–400 tokens per page
• Rasterized image: ~1,600 tokens per page (at 150 DPI)
• Both together: ~2,000–2,400 tokens per page

For a 100-page PDF, rasterizing everything would consume ~160K tokens. Only rasterize pages that matter for the question at hand.

Choosing your reading strategy

Text-heavy documents (reports, articles, books): → Text extraction is primary. Rasterize only for specific figures or pages where layout matters.

Scanned documents (pdffonts shows no fonts): → pdftotext will return nothing — don't run it. Rasterize pages at 150 DPI and Read them visually. For bulk text extraction, use OCR (pytesseract after converting pages to images — see REFERENCE.md for a complete example).

Slide-deck PDFs (exported presentations): → Every page is primarily visual. Rasterize individual pages on demand. Text extraction gives you bullet-point text but loses all layout.

Form-heavy documents: → Extract form field values programmatically first (see below). Rasterize the form page for visual context if needed.

Data-heavy documents (tables, charts, figures): → Use pdfplumber for tables. Rasterize pages with charts/figures. Extract text for surrounding narrative. Consider both text AND image for the same page when precision matters.

Extracting embedded images

# List all embedded images with metadata (size, color, compression)
pdfimages -list document.pdf

# Extract all images as PNG
pdfimages -png document.pdf /tmp/img

# Extract from specific pages only (pages 3-5)
pdfimages -png -f 3 -l 5 document.pdf /tmp/img

# Extract in original format (JPEG stays JPEG, etc.)
pdfimages -all document.pdf /tmp/img

Then Read /tmp/img-000.png (etc.) to see each extracted image.

Gotcha — vector graphics: pdfimages extracts only raster image data. Charts and diagrams drawn as vector graphics (common in matplotlib, Excel, and R exports) will NOT appear — they are page content operators, not image objects. For these, rasterize the whole page with pdftoppm instead.

Gotcha — empty images: pdfimages sometimes produces many tiny or empty image files — these are typically background masks, transparency layers, or decorative elements. Filter by file size to find the real content images.

Programmatic extraction with position data:

import fitz  # PyMuPDF

doc = fitz.open("document.pdf")
for page in doc:
    for img in page.get_images():
        xref = img[0]
        pix = fitz.Pixmap(doc, xref)
        if pix.n - pix.alpha > 3:  # CMYK or other non-RGB
            pix = fitz.Pixmap(fitz.csRGB, pix)
        pix.save(f"/tmp/img_{xref}.png")

Extracting file attachments

PDFs can contain embedded files — spreadsheets, data files, other documents. Common in business reports, PDF portfolios, and PDF/A-3 compliance documents.

# List all attachments
pdfdetach -list document.pdf

# Extract all attachments to a directory
mkdir -p /tmp/attachments
pdfdetach -saveall -o /tmp/attachments/ document.pdf

# Extract a specific attachment by number (1-based index from -list output)
pdfdetach -save 1 -o /tmp/attachment.pdf document.pdf

In Python:

import os
from pypdf import PdfReader

reader = PdfReader("document.pdf")
for name, content_list in reader.attachments.items():
    safe_name = os.path.basename(name)  # sanitize — name comes from the PDF
    for content in content_list:
        with open(f"/tmp/{safe_name}", "wb") as f:
            f.write(content)

Two attachment mechanisms exist in PDFs: page-level file annotation attachments (shown as paperclip icons in viewers) and document-level embedded files (in the EmbeddedFiles name tree). Both pdfdetach and pypdf handle the common cases. Rich media assets (3D, video) embedded as annotations may not appear in the attachment list — use PyMuPDF to iterate page annotations for those.

Extracting form field data

PDFs with interactive forms (government forms, applications, contracts) have fillable fields whose values can be read programmatically:

from pypdf import PdfReader

reader = PdfReader("form.pdf")

# Text input fields only:
fields = reader.get_form_text_fields()
for name, value in fields.items():
    print(f"{name}: {value}")

# All field types (checkboxes, radio buttons, dropdowns too):
all_fields = reader.get_fields() or {}
for name, field in all_fields.items():
    print(f"{name}: {field.get('/V', '')} (type: {field.get('/FT', '')})")

getformtextfields() returns only text input fields. For government forms and contracts that use checkboxes, radio buttons, and dropdowns, use getfields() instead to see all field types.

For comprehensive field info (types, options, defaults):

pdftk form.pdf dump_data_fields

For anything beyond reading form data — filling forms, creating forms — use the pdf skill — invoke it by name if you have a Skill tool, or Read its SKILL.md (listed in your available skills, or in the same skills directory as this file).

Audio, video, and other rare embedded content