How to Merge PDF Files on Linux Command Line (pdfunite)

You can merge PDF files on Linux command line in seconds using pdfunite from the poppler-utils package. It is the fastest way to combine PDFs when you are working in a terminal, running batch scripts on a headless server, or automating document pipelines. This guide covers pdfunite in depth, then shows when to reach for alternatives like qpdf (preserves bookmarks and hyperlinks) and Ghostscript (compresses output). If you work with PDFs regularly from the terminal, these are essential Linux commands to have in your toolkit.

What is poppler-utils?

Poppler-utils is a set of command-line utilities built on the poppler PDF library (a fork of xpdf). It ships with most Linux distros and includes six tools:

This article focuses on pdfunite for merging, with coverage of the other tools where they help in a merge workflow (like pdfinfo for verification).

How to install poppler-utils on Linux

Poppler-utils is in the official repos of every major distro. Install it with your package manager.

sudo apt install poppler-utils

sudo dnf install poppler-utils

sudo pacman -S poppler

sudo zypper install poppler-tools

sudo apk add poppler-utils

brew install poppler

pdfunite version 24.02.0
Copyright 2005-2024 The Poppler Developers - http://poppler.freedesktop.org
Copyright 1996-2011 Glyph & Cog, LLC

How to merge PDF files with pdfunite

Basic syntax

The syntax is simple: list the input PDFs first, then the output filename last.

pdfunite file1.pdf file2.pdf file3.pdf output.pdf

This concatenates file1.pdf, file2.pdf, and file3.pdf in that order into output.pdf.

Merging with wildcards

You can use shell globbing to merge all PDFs in a directory:

pdfunite *.pdf output.pdf

Merging from a file list

If you have a text file listing the PDFs you want to merge (one filename per line), note that pdfunite does not support reading from stdin via a - flag. Use command substitution instead.

Simple approach (works if filenames have no spaces):

pdfunite $(cat files.txt) output.pdf

Safer approach (handles filenames with spaces):

mapfile -t files < files.txt
pdfunite "${files[@]}" output.pdf

The files.txt file should contain one PDF path per line:

report-intro.pdf
report-chapter1.pdf
report-chapter2.pdf
report-appendix.pdf

Verify the merge

After merging, check the page count to confirm all pages are present:

pdfinfo output.pdf | grep "^Pages:"

Compare against the sum of individual page counts:

pdfinfo file1.pdf | grep "^Pages:"
pdfinfo file2.pdf | grep "^Pages:"
pdfinfo output.pdf | grep "^Pages:"   # should equal the sum

Also check the file is not empty:

ls -lh output.pdf

Limitations of pdfunite (what you should know)

pdfunite is fast and simple, but it concatenates PDFs at the page content level. This means:

• Hyperlinks are lost. Internal TOC links and cross-references break after merging.
• Bookmarks/outlines are stripped. PDF outlines (the sidebar navigation in viewers like Evince or Acrobat) disappear.
• No encryption support. You cannot merge password-protected PDFs directly.
• No page manipulation. You cannot rotate, reorder, or extract specific pages.
• No compression. The output file can be larger than expected.

For simple merges (combining invoices, scanned pages, or reports without internal links), pdfunite is the right tool. If you need bookmarks or hyperlinks to survive, switch to qpdf.

Alternative tools for merging PDFs on Linux

When pdfunite is not enough, these three tools cover the gaps.

# Debian / Ubuntu
sudo apt install qpdf

# RHEL / Fedora
sudo dnf install qpdf

# Arch Linux
sudo pacman -S qpdf

qpdf --empty --pages file1.pdf file2.pdf file3.pdf -- output.pdf

# Pages 1-5 from file1, all pages from file2
qpdf --empty --pages file1.pdf 1-5 file2.pdf 1-z -- output.pdf

qpdf --decrypt --password=SECRET encrypted.pdf decrypted.pdf
pdfunite decrypted.pdf other.pdf merged.pdf

# Debian / Ubuntu
sudo apt install ghostscript

# RHEL / Fedora
sudo dnf install ghostscript

# Arch Linux
sudo pacman -S ghostscript

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite \
   -dPDFSETTINGS=/ebook \
   -sOutputFile=merged.pdf file1.pdf file2.pdf

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
   -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH \
   -sOutputFile=compressed.pdf merged.pdf

# Via pip (any distro)
pip install stapler

# Fedora
sudo dnf install pdf-stapler

stapler sel file1.pdf file2.pdf output.pdf

Tool comparison table

Real-world workflows and automation

Batch merge script with validation

This script validates all input files exist, merges them, and reports the page count:

#!/bin/bash
set -euo pipefail

OUTPUT="${1:-merged.pdf}"
shift

# Validate all inputs exist
for f in "$@"; do
    [[ -f "$f" ]] || { echo "ERROR: File not found: $f" >&2; exit 1; }
done

pdfunite "$@" "$OUTPUT"
echo "Created: $OUTPUT ($(pdfinfo "$OUTPUT" | grep "^Pages:" | awk '{print $2}') pages)"

Usage:

chmod +x merge-pdfs.sh
./merge-pdfs.sh combined-report.pdf chapter1.pdf chapter2.pdf chapter3.pdf

For more advanced automation workflows, you can integrate PDF processing into tools like n8n for document processing pipelines.

Handling encrypted PDFs

pdfunite cannot process password-protected PDFs. Decrypt them first with qpdf:

# Decrypt
qpdf --decrypt --password=THEPASS protected.pdf unprotected.pdf

# Then merge as usual
pdfunite unprotected.pdf other.pdf merged.pdf

# Clean up the decrypted file
rm unprotected.pdf

Verifying the merge

Always verify after merging, especially in scripts:

# Check total page count matches sum of inputs
EXPECTED=$(pdfinfo file1.pdf | grep "^Pages:" | awk '{sum += $2} END {print sum}')
EXPECTED=$((EXPECTED + $(pdfinfo file2.pdf | grep "^Pages:" | awk '{print $2}')))
ACTUAL=$(pdfinfo output.pdf | grep "^Pages:" | awk '{print $2}')

if [[ "$EXPECTED" -eq "$ACTUAL" ]]; then
    echo "OK: $ACTUAL pages"
else
    echo "MISMATCH: expected $EXPECTED, got $ACTUAL" >&2
    exit 1
fi

Keeping poppler-utils updated (security)

# Debian / Ubuntu
sudo apt update && sudo apt upgrade poppler-utils

# RHEL / Fedora
sudo dnf upgrade poppler-utils

Troubleshooting common errors

# Check permissions
ls -l file.pdf

# Fix: give owner read+write
chmod u+rw file.pdf

# Check your working directory
pwd

# List PDFs in the current directory
ls *.pdf

# Use tab completion to avoid typos
pdfunite file1<TAB>

qpdf --check damaged.pdf
qpdf --qdf damaged.pdf repaired.pdf

gs -o repaired.pdf -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress damaged.pdf

pdftk damaged.pdf output repaired.pdf

which pdfunite
# No output = not installed

# Check available memory
free -h

# Monitor swap usage
swapon --show

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite \
   -dPDFSETTINGS=/prepress \
   -sOutputFile=merged.pdf large1.pdf large2.pdf

Conclusion

For merging PDF files on the Linux command line, the tool you pick depends on what you need:

• pdfunite: default choice for simple merges. Fast, tiny, already installed on most systems.
• qpdf: use when bookmarks, hyperlinks, or encrypted PDFs are involved.
• Ghostscript: use when you need to compress the output or merge very large files.
• stapler: use when you need pdftk-style page manipulation.

Companion poppler tools are useful in a merge workflow: pdfinfo to check page counts and encryption status before merging, pdfseparate to split a PDF (the reverse operation), and pdftotext to extract text for verification.

If you run a VPS or headless server and process PDFs regularly, keep poppler-utils updated and consider securing your Linux server if it handles files from external sources.

FAQ

qpdf --decrypt --password=THEPASS protected.pdf unprotected.pdf
pdfunite unprotected.pdf other.pdf merged.pdf

qpdf --empty --pages file1.pdf file2.pdf -- output.pdf

pdfunite intro.pdf chapter1.pdf chapter2.pdf appendix.pdf output.pdf