In one of our Rails application, we needed to generate password protected PDFs. We used wicked_pdf (an awesome gem that generates PDFs from HTML template) to generate PDFs but it doesn't provide feature to secure it.

While searching for solution to secure PDFs we came across PDFtk (PDF toolkit). It is a cross-platform tool for manipulating PDF documents. It has feature to add password to PDF document using "user password" as well as "master password" (owner password) which is great.

Installing PDFtk

You need to install "PDFtk Server" which is a command-line tool for working with PDFs. More info & download instructions are nicely described here

Working with PDFtk

Usage of PDFtk Server is described here. Since we want to add password we need to run following statement on terminal.

pdftk <input PDF path> output <output PDF path> owner_pw <master password> user_pw <user password>

Example - pdftk test.pdf output test_password.pdf owner_pw master user_pw user

  • test.pdf is the input PDF that needs to be secured
  • test_password.pdf is the name of secured PDF to be generated
  • master is the master password of the PDF (optional)
  • user is the user password which will be shared to end user

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Note - owner_pw is optional.

Make it work with Rails

Above command should be ran on terminal. Now we need to make it run with Rails.

Ruby comes with a module Open3. We can use its popen3 method to run our PDFtk command-line statement.

Open3.popen3("<command>") do |_stdin, _stdout, stderr|
  // something to do in case of error (stderr)

Hope this helps.