Merge Multiple PDF Files Automatically Using Python

Merging multiple PDF documents into a single file can be fully automated using Python's modern pypdf library (the actively maintained successor to PyPDF2). This guide covers batch-merging an entire folder, merging files in a custom sequence, and extracting specific page ranges.

Prerequisites and Installation

Install pypdf using pip. It has no external C-dependencies and runs natively across all major platforms.

pip install pypdf

Method 1: Merge All PDFs in a Folder Automatically

To batch-merge every PDF inside a target directory, use Python's built-in pathlib module alongside pypdf.PdfMerger. This script scans the folder, sorts files alphabetically, and exports a unified PDF.

from pathlib import Path
from pypdf import PdfMerger

def merge_folder_pdfs(input_folder: str, output_path: str) -> None:
    target_dir = Path(input_folder)
    merger = PdfMerger()
    
    # Locate and sort all .pdf files in target_dir
    pdf_files = sorted(target_dir.glob("*.pdf"))
    
    if not pdf_files:
        raise FileNotFoundError(f"No PDF files found in {input_folder}")
        
    for pdf_path in pdf_files:
        merger.append(str(pdf_path))
        
    # Export merged file and clean up resources
    merger.write(output_path)
    merger.close()

# Example usage
merge_folder_pdfs("./input_pdfs", "combined_document.pdf")

If you need to sort files by modification date rather than filename, replace sorted(target_dir.glob("*.pdf")) with:

pdf_files = sorted(target_dir.glob("*.pdf"), key=lambda p: p.stat().st_mtime)

Method 2: Merge Specific PDFs in Custom Order

When combining specific files where document sequence matters (such as combining a title page, body content, and appendix), pass an explicit list of paths to the merger instance.

from pypdf import PdfMerger

def merge_pdf_list(file_paths: list[str], output_path: str) -> None:
    merger = PdfMerger()
    
    for pdf in file_paths:
        merger.append(pdf)
        
    merger.write(output_path)
    merger.close()

# Example usage
files_in_order = [
    "01_cover_page.pdf",
    "02_executive_summary.pdf",
    "03_financial_report.pdf"
]

merge_pdf_list(files_in_order, "final_compiled_report.pdf")

Method 3: Extract and Merge Specific Page Ranges

To pull partial sections from different PDFs, use the pages parameter in merger.append(). The argument accepts a zero-indexed tuple formatted as (start_page, end_page).

from pypdf import PdfMerger

merger = PdfMerger()

# Append pages 0 to 4 (page index 5 excluded) from first doc
merger.append("document_a.pdf", pages=(0, 5))

# Append pages 10 to 14 from second doc
merger.append("document_b.pdf", pages=(10, 15))

merger.write("selected_pages_merged.pdf")
merger.close()

Handling Edge Cases

• Encrypted PDFs: If a source PDF is password-protected, open it via PdfReader, call reader.decrypt("password"), and append the decrypted reader object instead of the file path.
• Legacy Outlines/Bookmarks: By default, pypdf preserves table-of-contents bookmarks. Pass import_outline=False into merger.append() to strip existing outlines and decrease output file size.
• Memory Footprint: For extremely large batches (hundreds of PDFs), close the merger instance using a try...finally block or explicit merger.close() to prevent open file handles from consuming system RAM.

Need this done fast? order this script on FreelanceHunt.