PDF

PDF Processing Guide

Overview

This guide covers essential PDF processing operations using Python libraries and command-line tools. For advanced features, JavaScript libraries, and detailed examples, see reference.md. If you need to fill out a PDF form, read forms.md and follow its instructions.

Quick Start

from pypdf import PdfReader, PdfWriter

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

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

Python Libraries

pypdf - Basic Operations

Merge PDFs

from pypdf import PdfWriter, PdfReader

writer = PdfWriter()
for pdf_file in ["doc1.pdf", "doc2.pdf", "doc3.pdf"]:
    reader = PdfReader(pdf_file)
    for page in reader.pages:
        writer.add_page(page)

with open("merged.pdf", "wb") as output:
    writer.write(output)

Split PDF

reader = PdfReader("input.pdf")
for i, page in enumerate(reader.pages):
    writer = PdfWriter()
    writer.add_page(page)
    with open(f"page_{i+1}.pdf", "wb") as output:
        writer.write(output)

Extract Metadata

reader = PdfReader("document.pdf")
meta = reader.metadata
print(f"Title: {meta.title}")
print(f"Author: {meta.author}")
print(f"Subject: {meta.subject}")
print(f"Creator: {meta.creator}")

Rotate Pages

reader = PdfReader("input.pdf")
writer = PdfWriter()

page = reader.pages[0]
page.rotate(90)  # Rotate 90 degrees clockwise
writer.add_page(page)

with open("rotated.pdf", "wb") as output:
    writer.write(output)

pdfplumber - Text and Table Extraction

Extract Text with Layout

import pdfplumber

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

Extract Tables

with pdfplumber.open("document.pdf") as pdf:
    for i, page in enumerate(pdf.pages):
        tables = page.extract_tables()
        for j, table in enumerate(tables):
            print(f"Table {j+1} on page {i+1}:")
            for row in table:
                print(row)

Advanced Table Extraction

import pandas as pd

with pdfplumber.open("document.pdf") as pdf:
    all_tables = []
    for page in pdf.pages:
        tables = page.extract_tables()
        for table in tables:
            if table:  # Check if table is not empty
                df = pd.DataFrame(table[1:], columns=table[0])
                all_tables.append(df)

# Combine all tables
if all_tables:
    combined_df = pd.concat(all_tables, ignore_index=True)
    combined_df.to_excel("extracted_tables.xlsx", index=False)

reportlab - Create PDFs

⚠️ CRITICAL: CJK (Chinese/Japanese/Korean) Font Support

The default reportlab fonts do NOT support CJK characters. If your content contains any Chinese, Japanese, or Korean text, you MUST register a CJK font first. Failing to do so will result in garbled text or missing characters in the output PDF.

CJK Font Registration (REQUIRED for Chinese/Japanese/Korean content)

IMPORTANT: Always call register_cjk_fonts() before creating any PDF that may contain CJK text.

import os
import glob
from reportlab.pdfbase import pdfmetrics
from reportlab.pdfbase.ttfonts import TTFont
from reportlab.pdfbase.cidfonts import UnicodeCIDFont
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.fonts import addMapping

# --- CJK font name constant (use this everywhere in your code) ---
CJK_FONT_NAME = "ChineseSans"  # Will be registered below

def register_cjk_fonts():
    """Register CJK fonts for reportlab. Call this ONCE before creating any PDF."""
    global CJK_FONT_NAME
    
    # Try to find system CJK fonts in common locations
    font_search_paths = [
        # macOS
        "/System/Library/Fonts/STHeiti Medium.ttc",
        "/System/Library/Fonts/PingFang.ttc",
        "/Library/Fonts/Microsoft/msyh.ttf",
        "/Library/Fonts/Arial Unicode.ttf",
        # Linux (Docker / Ubuntu / Debian)
        "/usr/share/fonts/truetype/noto/NotoSansCJK-Regular.ttc",
        "/usr/share/fonts/opentype/noto/NotoSansCJK-Regular.ttc",
        "/usr/share/fonts/truetype/wqy/wqy-zenhei.ttc",
        "/usr/share/fonts/truetype/wqy/wqy-microhei.ttc",
        "/usr/share/fonts/truetype/droid/DroidSansFallbackFull.ttf",
        # Windows
        "C:/Windows/Fonts/msyh.ttf",
        "C:/Windows/Fonts/simsun.ttc",
    ]
    
    # Also search common font directories recursively for CJK fonts
    font_dirs = [
        "/usr/share/fonts",
        "/System/Library/Fonts",
        "/Library/Fonts",
    ]
    for font_dir in font_dirs:
        if os.path.isdir(font_dir):
            for ext in ("*.ttf", "*.ttc", "*.otf"):
                for path in glob.glob(os.path.join(font_dir, "**", ext), recursive=True):
                    name_lower = os.path.basename(path).lower()
                    if any(kw in name_lower for kw in ("noto", "cjk", "wqy", "hei", "song", "ming", "gothic", "ping")):
                        font_search_paths.append(path)
    
    for font_path in font_search_paths:
        if os.path.exists(font_path):
            try:
                pdfmetrics.registerFont(TTFont(CJK_FONT_NAME, font_path))
                # Also register bold/italic variants using the same font
                pdfmetrics.registerFont(TTFont(f"{CJK_FONT_NAME}-Bold", font_path))
                addMapping(CJK_FONT_NAME, 0, 0, CJK_FONT_NAME)       # normal
                addMapping(CJK_FONT_NAME, 1, 0, f"{CJK_FONT_NAME}-Bold")  # bold
                addMapping(CJK_FONT_NAME, 0, 1, CJK_FONT_NAME)       # italic
                addMapping(CJK_FONT_NAME, 1, 1, f"{CJK_FONT_NAME}-Bold")  # bold-italic
                print(f"Registered CJK font: {font_path}")
                return True
            except Exception as e:
                print(f"Failed to register font {font_path}: {e}")
                continue
    
    # Fallback: use reportlab built-in CID font (less pretty but works)
    try:
        pdfmetrics.registerFont(UnicodeCIDFont('STSong-Light'))
        CJK_FONT_NAME = "STSong-Light"
        print("Registered fallback CID font: STSong-Light")
        return True
    except Exception:
        pass
    
    print("WARNING: No CJK fonts found. Chinese text may not render correctly.")
    return False


def get_cjk_styles():
    """Get reportlab styles with CJK font applied to all text styles."""
    styles = getSampleStyleSheet()
    
    # Override all standard styles with CJK font
    for style_name in ['Normal', 'BodyText', 'Italic', 'Title', 'Heading1', 
                        'Heading2', 'Heading3', 'Heading4', 'Heading5', 'Heading6',
                        'Bullet', 'Definition', 'Code', 'UnorderedList', 'OrderedList']:
        if style_name in styles:
            styles[style_name].fontName = CJK_FONT_NAME
    
    return styles

Usage Example - PDF with Chinese Text

# ALWAYS register CJK fonts first!
register_cjk_fonts()

from reportlab.lib.pagesizes import A4
from reportlab.platypus import SimpleDocTemplate, Paragraph, Spacer, PageBreak

# Use CJK-enabled styles
styles = get_cjk_styles()

doc = SimpleDocTemplate("chinese_report.pdf", pagesize=A4)
story = []

story.append(Paragraph("学术论文标题", styles['Title']))
story.append(Spacer(1, 12))
story.append(Paragraph("这是正文内容。中文字符可以正常显示。", styles['Normal']))

doc.build(story)

Basic PDF Creation (English only)

from reportlab.lib.pagesizes import letter
from reportlab.pdfgen import canvas

c = canvas.Canvas("hello.pdf", pagesize=letter)
width, height = letter

# Add text
c.drawString(100, height - 100, "Hello World!")
c.drawString(100, height - 120, "This is a PDF created with reportlab")

# Add a line
c.line(100, height - 140, 400, height - 140)

# Save
c.save()

Create PDF with Multiple Pages

from reportlab.lib.pagesizes import letter
from reportlab.platypus import SimpleDocTemplate, Paragraph, Spacer, PageBreak
from reportlab.lib.styles import getSampleStyleSheet

# NOTE: If your content contains Chinese/Japanese/Korean text,
# replace getSampleStyleSheet() with get_cjk_styles() and 
# call register_cjk_fonts() first! See CJK section above.

doc = SimpleDocTemplate("report.pdf", pagesize=letter)
styles = getSampleStyleSheet()
story = []

# Add content
title = Paragraph("Report Title", styles['Title'])
story.append(title)
story.append(Spacer(1, 12))

body = Paragraph("This is the body of the report. " * 20, styles['Normal'])
story.append(body)
story.append(PageBreak())

# Page 2
story.append(Paragraph("Page 2", styles['Heading1']))
story.append(Paragraph("Content for page 2", styles['Normal']))

# Build PDF
doc.build(story)

Command-Line Tools

pdftotext (poppler-utils)

# Extract text
pdftotext input.pdf output.txt

# Extract text preserving layout
pdftotext -layout input.pdf output.txt

# Extract specific pages
pdftotext -f 1 -l 5 input.pdf output.txt  # Pages 1-5

qpdf

# Merge PDFs
qpdf --empty --pages file1.pdf file2.pdf -- merged.pdf

# Split pages
qpdf input.pdf --pages . 1-5 -- pages1-5.pdf
qpdf input.pdf --pages . 6-10 -- pages6-10.pdf

# Rotate pages
qpdf input.pdf output.pdf --rotate=+90:1  # Rotate page 1 by 90 degrees

# Remove password
qpdf --password=mypassword --decrypt encrypted.pdf decrypted.pdf

pdftk (if available)

# Merge
pdftk file1.pdf file2.pdf cat output merged.pdf

# Split
pdftk input.pdf burst

# Rotate
pdftk input.pdf rotate 1east output rotated.pdf

Common Tasks

Extract Text from Scanned PDFs

# Requires: pip install pytesseract pdf2image
import pytesseract
from pdf2image import convert_from_path

# Convert PDF to images
images = convert_from_path('scanned.pdf')

# OCR each page
text = ""
for i, image in enumerate(images):
    text += f"Page {i+1}:\n"
    text += pytesseract.image_to_string(image)
    text += "\n\n"

print(text)

Add Watermark

from pypdf import PdfReader, PdfWriter

# Create watermark (or load existing)
watermark = PdfReader("watermark.pdf").pages[0]

# Apply to all pages
reader = PdfReader("document.pdf")
writer = PdfWriter()

for page in reader.pages:
    page.merge_page(watermark)
    writer.add_page(page)

with open("watermarked.pdf", "wb") as output:
    writer.write(output)

Extract Images

# Using pdfimages (poppler-utils)
pdfimages -j input.pdf output_prefix

# This extracts all images as output_prefix-000.jpg, output_prefix-001.jpg, etc.

Password Protection

from pypdf import PdfReader, PdfWriter

reader = PdfReader("input.pdf")
writer = PdfWriter()

for page in reader.pages:
    writer.add_page(page)

# Add password
writer.encrypt("userpassword", "ownerpassword")

with open("encrypted.pdf", "wb") as output:
    writer.write(output)

Quick Reference

Next Steps

• For advanced pypdfium2 usage, see reference.md
• For JavaScript libraries (pdf-lib), see reference.md
• If you need to fill out a PDF form, follow the instructions in forms.md
• For troubleshooting guides, see reference.md