Merge PDF Files in Order with pdfunite

You will finish with one PDF containing the pages from several source files in the order you choose. The examples use pdfunite 24.02.0 from poppler-utils 24.02.0-1ubuntu9.9, as installed on this machine.

Allow about ten minutes. You need readable PDF files, enough free space for the destination, and permission to write to its directory. The normal workflow is unprivileged. Do not use sudo unless the input or destination is genuinely protected by filesystem permissions.

1. Check the installed command

Confirm which executable is on your path and record its version. These are read-only checks:

$ command -v pdfunite
/usr/bin/pdfunite
$ pdfunite -v
pdfunite version 24.02.0
Copyright 2005-2024 The Poppler Developers - http://poppler.freedesktop.org
Copyright 1996-2011, 2022 Glyph & Cog, LLC

The command accepts source files followed by one destination file. Its documented options are for version and usage information: -v, -h, -help and --help. The merge itself is controlled by the file arguments, not by a format or page-range switch.

2. Inspect the inputs before merging

List the files you intend to combine and ask pdfinfo for a quick, read-only check. Replace the example paths with your own files:

$ ls -lh /path/to/report-cover.pdf /path/to/report-body.pdf /path/to/report-appendix.pdf
$ pdfinfo /path/to/report-cover.pdf | sed -n '1,14p'
Title:           Report cover
Pages:           1
Encrypted:       no

The exact metadata varies. The useful fields are a plausible page count and Encrypted: no. The pdfunite manual says that source PDFs must not be encrypted. If a source is encrypted, obtain an authorised unencrypted copy or use the document owner's approved workflow. Do not try to bypass a password or access control.

Check every source, not just the first one. This catches a misspelled path and an encrypted appendix before you create a result:

$ for file in /path/to/report-cover.pdf /path/to/report-body.pdf /path/to/report-appendix.pdf; do
>   printf '%s: ' "$file"
>   pdfinfo "$file" | awk -F': *' '/^Pages:/ { print $2; found=1 } /^Encrypted:/ { print $2; found=1 } END { if (!found) exit 1 }'
> done
/path/to/report-cover.pdf: 1
no
/path/to/report-body.pdf: 8
no
/path/to/report-appendix.pdf: 3
no

If pdfinfo cannot open a file, stop and fix the path or read permission. A failed inspection is not a reason to add sudo automatically.

3. Choose a new destination

Pick a destination that is not one of the source files. This makes the operation easier to review and avoids confusing an input with the result:

$ destination=/path/to/report-merged.pdf
$ test ! -e "$destination" && echo "destination is new"
destination is new

This check does not create the file. If the destination already exists, choose another name or make an explicit, recoverable backup first. Do not overwrite a useful document as part of a blind script. If you do make a backup, retain it until the merged PDF has been opened and checked; deleting that backup is irreversible.

4. Merge the PDFs

Run one ordinary command with all sources first and the destination last:

$ pdfunite \
>   /path/to/report-cover.pdf \
>   /path/to/report-body.pdf \
>   /path/to/report-appendix.pdf \
>   "$destination"

A successful run normally returns to the shell without a progress report. The command reads all pages from the first source, then all pages from the second, and so on. It does not ask you to select pages interactively.

There is no persistent service or configuration change to undo. If the result is wrong, keep the source files, choose a different destination, correct the argument order and run the command again. If an incomplete destination was created after an error, do not treat it as a valid document: move it aside using your normal file-recovery procedure and preserve it until you have established whether it is needed for diagnosis.

5. Verify the result

Check that the output exists, is readable as a PDF, and has the expected page count:

$ pdfinfo "$destination" | sed -n '1,14p'
Pages:           12
Encrypted:       no
PDF version:     1.5
$ test -s "$destination" && echo "merged PDF is non-empty"
merged PDF is non-empty

In this example, the source page counts were 1, 8 and 3, so 12 pages is the expected total. Calculate the total for your own inputs rather than copying that number. A readable file and a successful exit status do not prove that every page looks right, so open the result in a trusted PDF viewer and check the boundaries between source documents.

If the page count is unexpected, inspect each source again and compare the command with your written order. If pdfunite reports an error, preserve the source files, read the error literally, and check paths, permissions and encryption before changing anything else. The installed command has no option that repairs a damaged or encrypted source.

6. Use help when a script needs a contract

For a script or a new machine, capture the local usage text rather than assuming that another Poppler build has identical packaging:

$ pdfunite --help 2>&1 | sed -n '1,12p'
pdfunite version 24.02.0
Usage: pdfunite [options] <PDF-sourcefile-1>..<PDF-sourcefile-n> <PDF-destfile>
  -v             : print copyright and version info
  -h             : print usage information
  -help          : print usage information
  --help         : print usage information

Quote paths in shell scripts, especially paths containing spaces. Keep the source list explicit when document order matters, and check exit status before passing the destination to another process. Do not feed untrusted file names into an unreviewed command line.