CombinePDF - the ruby way for merging PDF files

Gem Version GitHub Documentation

CombinePDF is a nifty model, written in pure Ruby, to parse PDF files and combine (merge) them with other PDF files, watermark them, or stamp them (all using the PDF file format and pure Ruby code).

Maintained (For Personal Purpose)

The original creator and maintainer boazsegev has stopped maintaining this gem. Let's agree that the man has done enough to create and maintain this gem for such a long time, providing feature for free since 2014. This fork is just for my purpose as I need to fix some errors and issues fixed in a somewhat hacky manner.


Install with ruby gems:

gem install combine_pdf

Known Limitations

Quick rundown by the creator(boazsegev) himself:

  • When reading PDF Forms, some form data might be lost. I tried fixing this to the best of my ability, but I'm not sure it all works just yet.

  • When combining PDF Forms, form data might be unified. I couldn't fix this because this is how PDF forms work (filling a field fills in the data in any field with the same name), but frankly, I kinda liked the issue... it's almost a feature.

  • When unifying the same TOC data more than once, one of the references will be unified with the other (meaning that if the pages look the same, both references will link to the same page instead of linking to two different pages). You can fix this by adding content to the pages before merging the PDF files (i.e. add empty text boxes to all the pages).

  • Some links and data (URL links and PDF "Named Destinations") are stored at the root of a PDF and they aren't linked back to the page. Keeping this information requires merging the PDF objects rather than their pages.

Some links will be lost when ripping pages out of PDF files and merging them with another PDF.

  • Some encrypted PDF files (usually the ones you can't view without a password) will fail quietly instead of noisily. If you prefer to choose the noisy route, you can specify the raise_on_encrypted option using CombinePDF.load(pdf_file, raise_on_encrypted: true) which will raise a CombinePDF::EncryptionError.

  • Sometimes the CombinePDF will raise an exception even if the PDF could be parsed (i.e., when PDF optional content exists)... I find it better to err on the side of caution, although for optional content PDFs an exception is avoidable using CombinePDF.load(pdf_file, allow_optional_content: true).

  • The CombinePDF gem runs recursive code to both parse and format the PDF files. Hence, PDF files that have heavily nested objects, as well as those that were combined in a way that results in cyclic nesting, might explode the stack - resulting in an exception or program failure.

CombinePDF is written natively in Ruby and should (presumably) work on all Ruby platforms that follow Ruby 2.0 compatibility.

However, PDF files are quite complex creatures and no guarantee is provided.

For example, PDF Forms are known to have issues and form data might be lost when attempting to combine PDFs with filled form data (also, forms are global objects, not page specific, so one should combine the whole of the PDF for any data to have any chance of being preserved).

The same applies to PDF links and the table of contents, which all have global attributes and could be corrupted or lost when combining PDF data.

If this library causes loss of data or burns down your house, I'm not to blame - as pointed to by the MIT license. That being said, I'm using the library happily after testing against different solutions.

Combine/Merge PDF files or Pages

To combine PDF files (or data):

pdf =
pdf << CombinePDF.load("file1.pdf") # one way to combine, very fast.
pdf << CombinePDF.load("file2.pdf") "combined.pdf"

Or even a one-liner:

(CombinePDF.load("file1.pdf") << CombinePDF.load("file2.pdf") << CombinePDF.load("file3.pdf")).save("combined.pdf")

you can also add just odd or even pages:

pdf =
i = 0
CombinePDF.load("file.pdf").pages.each do |page|
  i += 1
  pdf << page if i.even?
end "even_pages.pdf"

Notice that adding all the pages one by one is slower than adding the whole file.

Add content to existing pages (Stamp / Watermark)

To add content to existing PDF pages, first import the new content from an existing PDF file. After that, add the content to each of the pages in your existing PDF.

In this example, we will add a company logo to each page:

 = CombinePDF.load("company_logo.pdf").pages[0]
pdf = CombinePDF.load "content_file.pdf"
pdf.pages.each {|page| page << } # notice the << operator is on a page and not a PDF object. "content_with_logo.pdf"

Notice the << operator is on a page and not a PDF object. The << operator acts differently on PDF objects and on Pages.

The << operator defaults to secure injection by renaming references to avoid conflicts. For overlaying pages using compressed data that might not be editable (due to limited filter support), you can use:

pdf.pages(nil, false).each {|page| page << stamp_page}

Page Numbering

Adding page numbers to a PDF object or file is as simple as can be:

pdf = CombinePDF.load "file_to_number.pdf"
pdf.number_pages "file_with_numbering.pdf"

Numbering can be done with many different options, with different formating, with or without a box object, and even with opacity values - see documentation.

For example, should you prefer to place the page number on the bottom right side of all PDF pages, do:

pdf.number_pages(location: [:bottom_right])

As another example, the dashes around the number are removed and a box is placed around it. The numbering is semi-transparent and the first 3 pages are numbered using letters (a,b,c) rather than numbers:

# Number the first 3 pages as "a", "b", "c"
pdf.number_pages(number_format: " %s ",
                 location: [:top, :bottom, :top_left, :top_right, :bottom_left, :bottom_right],
                 start_at: "a",
                 page_range: (0..2),
                 box_color: [0.8,0.8,0.8],
                 border_color: [0.4, 0.4, 0.4],
                 border_width: 1,
                 box_radius: 6,
                 opacity: 0.75)
# Number the rest of the pages as 4, 5, ... etc'
pdf.number_pages(number_format: " %s ",
                 location: [:top, :bottom, :top_left, :top_right, :bottom_left, :bottom_right],
                 start_at: 4,
                 page_range: (3..-1),
                 box_color: [0.8,0.8,0.8],
                 border_color: [0.4, 0.4, 0.4],
                 border_width: 1,
                 box_radius: 6,
                 opacity: 0.75)
pdf.number_pages(number_format: " %s ", location: :bottom_right, font_size: 44)

Loading and Parsing PDF data

Loading PDF data can be done from file system or directly from the memory.

Loading data from a file is easy:

pdf = CombinePDF.load("file.pdf")

You can also parse PDF files from memory. Loading from the memory is especially effective for importing PDF data received through the internet or from a different authoring library such as Prawn:

pdf_data = prawn_pdf_document.render # Import PDF data from Prawn
pdf = CombinePDF.parse(pdf_data)

Using parse is also effective when loading data from a remote location, circumventing the need for unnecessary temporary files. For example:

require 'combine_pdf'
require 'net/http'

url = ""
pdf = CombinePDF.parse Net::HTTP.get_response(URI.parse(url)).body

Rendering PDF data

Similarly, to loading and parsing, rendering can also be performed either to the memory or to a file.

You can output a string of PDF data using .to_pdf. For example, to let a user download the PDF from either a Rails application or a Plezi application:

# in a controller action
send_data combined_file.to_pdf, filename: "combined.pdf", type: "application/pdf"

In Sinatra:

# in your path's block
status 200
body combined_file.to_pdf
headers 'content-type' => "application/pdf"

If you prefer to save the PDF data to a file, you can always use the save method as we did in our earlier examples.

Some PDF files contain optional content sections which cannot always be merged reliably. By default, an exception is raised if one of these files are detected. You can optionally pass an allow_optional_content parameter to the, CombinePDF.load, and CombinePDF.parse methods:

new_pdf =
new_pdf << CombinePDF.load(pdf_file, allow_optional_content: true)
attachments.each { |att| new_pdf << CombinePDF.load(att, allow_optional_content: true) }


You can see a Demo for a "Bates stumping web-app" and read through it's code . Good luck :)

Decryption & Filters

Some PDF files are encrypted and some are compressed (the use of filters)...

There is very little support for encrypted files and very very basic and limited support for compressed files.

I need help with that.

Comments and file structure

If you want to help with the code, please be aware:

I'm a self-learned hobbyist at heart. The documentation is lacking and the comments in the code are poor guidelines.

The code itself should be very straightforward, but feel free to ask whatever you want.


Boaz Segev

Stefan Leitner (@sLe1tner) wrote the outline merging code supporting PDFs which contain a ToC. Caige Nichols wrote an amazing RC4 gem which I used in my code. I wanted to install the gem, but I had issues with the internet and ended up copying the code itself into the combine_pdf_decrypt class file. Credit to his wonderful is given here. Please respect his license and copyright... and mine.

Credit to Boaz Segev and his wonderful work, just working on it for few hacky solutions.




You can look at the GitHub Issues Page and see the "help wanted" tags.

If you're thinking of donations or sending me money - no need. This project can sustain itself without your money.

What this project needs is the time given by caring developers who keep it up to date and fix any documentation errors or issues they notice ... having said that, gifts (such as free coffee or iTunes gift cards) are always fun. But I think there are those in real need that will benefit more from your generosity.