add tool to merge pdf files

app/controllers/api/tools_controller.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Api
+  class ToolsController < ApiBaseController
+    skip_authorization_check
+
+    def merge
+      files = params[:files] || []
+
+      return render json: { error: 'Files are required' }, status: :unprocessable_entity if files.blank?
+      return render json: { error: 'At least 2 files are required' }, status: :unprocessable_entity if files.size < 2
+
+      render json: {
+        data: Base64.encode64(PdfUtils.merge(files.map { |base64| StringIO.new(Base64.decode64(base64)) }).string)
+      }
+    end
+  end
+end

config/routes.rb

@@ -41,6 +41,9 @@ Rails.application.routes.draw do
       resources :clone, only: %i[create], controller: 'templates_clone'
       resources :submissions, only: %i[index create]
     end
+    resources :tools, only: %i[] do
+      post :merge, on: :collection
+    end
   end
 
   resources :verify_pdf_signature, only: %i[create]

lib/pdf_utils.rb

@@ -26,4 +26,19 @@ module PdfUtils
 
     decrypted_io.tap(&:rewind).read
   end
+
+  def merge(files)
+    merged_pdf = HexaPDF::Document.new
+
+    files.each do |file|
+      pdf = HexaPDF::Document.new(io: file)
+      pdf.pages.each { |page| merged_pdf.pages << merged_pdf.import(page) }
+    end
+
+    merged_content = StringIO.new
+    merged_pdf.write(merged_content)
+    merged_content.rewind
+
+    merged_content
+  end
 end