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