Sample using iText via JRuby to render a PDF with layers.

pdf_layer_example.rb

require "java"
Dir["#{File.dirname(__FILE__)}/itext-5.3.5/\*.jar"].each { |jar| require jar }

import com.itextpdf.text.BaseColor
import com.itextpdf.text.Document
import com.itextpdf.text.Paragraph
import com.itextpdf.text.Element
import com.itextpdf.text.pdf.ColumnText
import com.itextpdf.text.pdf.PdfWriter
import com.itextpdf.text.pdf.PdfContentByte
import com.itextpdf.text.pdf.PdfLayer
import java.io.FileOutputStream

document = Document.new
paragraph_1 = Paragraph.new "This is Layer 1"
paragraph_2 = Paragraph.new "This is Layer 2"

writer = PdfWriter.getInstance(document, FileOutputStream.new("pdf_demo.pdf"))
writer.setPdfVersion(PdfWriter::VERSION_1_5)

document.open

cb = writer.getDirectContent

layer_1 = PdfLayer.new "Layer 1", writer
cb.beginLayer layer_1
ColumnText.showTextAligned(cb, Element.ALIGN_LEFT, paragraph_1, 50, 775, 0)
cb.endLayer

layer_2 = PdfLayer.new "Layer 2", writer
cb.beginLayer layer_2
ColumnText.showTextAligned(cb, Element.ALIGN_LEFT, paragraph_2, 100, 800, 0)
cb.endLayer

document.close