creating pdf/a files using this config file:<fop version="1.0">

<!-- Strict user configuration -->
  <strict-configuration>true</strict-configuration>

  <!-- Strict FO validation -->
  <strict-validation>true</strict-validation>

  <!-- Base URL for resolving relative URLs -->
  <base>./</base>

  <!-- Font Base URL for resolving relative font URLs -->
  <font-base>./</font-base>

  <!-- Source resolution in dpi (dots/pixels per inch) for determining the size of pixels in SVG and bitmap images, default: 72dpi -->
  <source-resolution>72</source-resolution>
  <!-- Target resolution in dpi (dots/pixels per inch) for specifying the target resolution for generated bitmaps, default: 72dpi -->
  <target-resolution>72</target-resolution>

  <!-- default page-height and page-width, in case
       value is specified as auto -->
  <default-page-settings height="11in" width="8.26in"/>

  <!-- etc. etc..... -->

  <renderers>
   <renderer mime="application/pdf">
   <fonts>
       <font kerning="no" embed-url="file:///C:/Users/jstaerk/temp/timesbd.ttf" embedding-mode="subset">
           <font-triplet name="Times" style="normal" weight="bold" />
       </font>
       <font kerning="no" embed-url="file:///C:/Users/jstaerk/temp/timesbd.ttf" embedding-mode="subset">
           <font-triplet name="SourceSerifPro" style="normal" weight="normal" />
       </font>
   </fonts>
   </renderer>
</renderers>

</fop>

library/src/main/java/org/mustangproject/ZUGFeRD/ZUGFeRDVisualizer.java

@@ -1,21 +1,23 @@
-/** **********************************************************************
+/**
- *
+ * *********************************************************************
+ * <p>
  * Copyright 2018 Jochen Staerk
- *
+ * <p>
  * Use is subject to license terms.
- *
+ * <p>
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy
  * of the License at http://www.apache.org/licenses/LICENSE-2.0.
- *
+ * <p>
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *
+ * <p>
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *
+ * <p>
- *********************************************************************** */
+ * **********************************************************************
+ */
 package org.mustangproject.ZUGFeRD;
 
 import javax.xml.transform.*;
@@ -36,6 +38,7 @@ public class ZUGFeRDVisualizer {
 		FR,
 		DE
 	}
+
 	static final ClassLoader CLASS_LOADER = ZUGFeRDVisualizer.class.getClassLoader();
 	private static final String RESOURCE_PATH = "";
 	private static final Logger LOG = Logger.getLogger(ZUGFeRDVisualizer.class.getName());
@@ -54,6 +57,7 @@ public class ZUGFeRDVisualizer {
 	private Templates mXsltXRTemplate = null;
 	private Templates mXsltUBLTemplate = null;
 	private Templates mXsltHTMLTemplate = null;
+	private Templates mXsltPDFTemplate = null;
 	private Templates mXsltZF1HTMLTemplate = null;
 
 	public ZUGFeRDVisualizer() {
@@ -66,13 +70,19 @@ public class ZUGFeRDVisualizer {
 			throws FileNotFoundException, TransformerException, UnsupportedEncodingException {
 
 		try {
-			if (mXsltXRTemplate==null) {
+			if (mXsltXRTemplate == null) {
 				mXsltXRTemplate = mFactory.newTemplates(
 						new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/cii-xr.xsl")));
 			}
-			mXsltHTMLTemplate = mFactory.newTemplates(new StreamSource(
+			if (mXsltPDFTemplate == null) {
-					CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/xrechnung-html."+lang.name().toLowerCase()+".xsl")));
+				mXsltPDFTemplate = mFactory.newTemplates(
-			if (mXsltZF1HTMLTemplate==null) {
+						new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/xr-pdf.xsl")));
+			}
+			if (mXsltHTMLTemplate == null) {
+				mXsltHTMLTemplate = mFactory.newTemplates(new StreamSource(
+						CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/xrechnung-html." + lang.name().toLowerCase() + ".xsl")));
+			}
+			if (mXsltZF1HTMLTemplate == null) {
 				mXsltZF1HTMLTemplate = mFactory.newTemplates(new StreamSource(
 						CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/ZUGFeRD_1p0_c1p0_s1p0.xslt")));
 			}
@@ -86,14 +96,14 @@ public class ZUGFeRDVisualizer {
 		 * http://www.ferd-net.de/upload/Dokumente/FACTUR-X_ZUGFeRD_2p0_Teil1_Profil_EN16931_1p03.pdf
 		 * http://countwordsfree.com/xmlviewer
 		 */
-		FileInputStream fis=new FileInputStream(xmlFilename);
+		FileInputStream fis = new FileInputStream(xmlFilename);
-		String fileContent="";
+		String fileContent = "";
 		try {
 			fileContent = new String(Files.readAllBytes(Paths.get(xmlFilename)), StandardCharsets.UTF_8);
 		} catch (IOException e2) {
 			LOG.log(Level.SEVERE, null, e2);
 		}
-		
+
 		ByteArrayOutputStream iaos = new ByteArrayOutputStream();
 		ByteArrayOutputStream baos = new ByteArrayOutputStream();
 
@@ -101,7 +111,7 @@ public class ZUGFeRDVisualizer {
 		String zf2Signature = "rsm:CrossIndustryInvoice";
 		String ublSignature = "ubl:Invoice";
 		String ublCreditNoteSignature = "ubl:CreditNote";
-		boolean doPostProcessing=false;
+		boolean doPostProcessing = false;
 		if (fileContent.contains(zf1Signature)) {
 			applyZF1XSLT(fis, baos);
 
@@ -109,16 +119,16 @@ public class ZUGFeRDVisualizer {
 
 			//zf2 or fx
 			applyZF2XSLT(fis, iaos);
-			doPostProcessing=true;
+			doPostProcessing = true;
 		} else if (fileContent.contains(ublSignature)) {
 			//zf2 or fx
 			applyUBL2XSLT(fis, iaos);
-			doPostProcessing=true;
+			doPostProcessing = true;
 
 		} else if (fileContent.contains(ublCreditNoteSignature)) {
 			//zf2 or fx
 			applyUBLCreditNote2XSLT(fis, iaos);
-			doPostProcessing=true;
+			doPostProcessing = true;
 
 		}
 		if (doPostProcessing) {
@@ -158,20 +168,88 @@ public class ZUGFeRDVisualizer {
 			}
 
 		}
-		
+
 		return baos.toString("UTF-8");
 	}
 
-	public void applyZF2XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
+	public String toFOP(String xmlFilename)
+			throws FileNotFoundException, TransformerException, UnsupportedEncodingException {
+
+		try {
+			if (mXsltXRTemplate == null) {
+				mXsltXRTemplate = mFactory.newTemplates(
+						new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/cii-xr.xsl")));
+			}
+			if (mXsltPDFTemplate == null) {
+				mXsltPDFTemplate = mFactory.newTemplates(
+						new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/xr-pdf.xsl")));
+			}
+		} catch (TransformerConfigurationException ex) {
+			LOG.log(Level.SEVERE, null, ex);
+		}
+
+		FileInputStream fis = new FileInputStream(xmlFilename);
+		String fileContent = "";
+		try {
+			fileContent = new String(Files.readAllBytes(Paths.get(xmlFilename)), StandardCharsets.UTF_8);
+		} catch (IOException e2) {
+			LOG.log(Level.SEVERE, null, e2);
+		}
+
+		ByteArrayOutputStream iaos = new ByteArrayOutputStream();
+		ByteArrayOutputStream baos = new ByteArrayOutputStream();
+
+		//zf2 or fx
+		applyZF2XSLT(fis, iaos);
+
+		PipedInputStream in = new PipedInputStream();
+		PipedOutputStream out;
+		try {
+			out = new PipedOutputStream(in);
+			new Thread(new Runnable() {
+				public void run() {
+					try {
+						// write the original OutputStream to the PipedOutputStream
+						// note that in order for the below method to work, you need
+						// to ensure that the data has finished writing to the
+						// ByteArrayOutputStream
+						iaos.writeTo(out);
+					} catch (IOException e) {
+						LOG.log(Level.SEVERE, null, e);
+					} finally {
+						// close the PipedOutputStream here because we're done writing data
+						// once this thread has completed its run
+						if (out != null) {
+							// close the PipedOutputStream cleanly
+							try {
+								out.close();
+							} catch (IOException e) {
+								// TODO Auto-generated catch block
+								LOG.log(Level.SEVERE, null, e);
+							}
+						}
+					}
+				}
+			}).start();
+			applyXSLTToPDF(in, baos);
+		} catch (IOException e1) {
+			LOG.log(Level.SEVERE, null, e1);
+		}
+
+
+		return baos.toString("UTF-8");
+	}
+
+	protected void applyZF2XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
 			throws TransformerException {
 		Transformer transformer = mXsltXRTemplate.newTransformer();
 
 		transformer.transform(new StreamSource(xmlFile), new StreamResult(HTMLOutstream));
 	}
 
-	public void applyUBL2XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
+	protected void applyUBL2XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
 			throws TransformerException {
-		if (mXsltUBLTemplate==null) {
+		if (mXsltUBLTemplate == null) {
 			mXsltUBLTemplate = mFactory.newTemplates(
 					new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/ubl-invoice-xr.xsl")));
 		}
@@ -180,9 +258,9 @@ public class ZUGFeRDVisualizer {
 		transformer.transform(new StreamSource(xmlFile), new StreamResult(HTMLOutstream));
 	}
 
-	public void applyUBLCreditNote2XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
+	protected void applyUBLCreditNote2XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
 			throws TransformerException {
-		if (mXsltUBLTemplate==null) {
+		if (mXsltUBLTemplate == null) {
 			mXsltUBLTemplate = mFactory.newTemplates(
 					new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/ubl-creditnote-xr.xsl")));
 		}
@@ -191,20 +269,27 @@ public class ZUGFeRDVisualizer {
 		transformer.transform(new StreamSource(xmlFile), new StreamResult(HTMLOutstream));
 	}
 
-	public void applyZF1XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
+	protected void applyZF1XSLT(final InputStream xmlFile, final OutputStream HTMLOutstream)
 			throws TransformerException {
 		Transformer transformer = mXsltZF1HTMLTemplate.newTransformer();
 
 		transformer.transform(new StreamSource(xmlFile), new StreamResult(HTMLOutstream));
 	}
 
-	public void applyXSLTToHTML(final InputStream xmlFile, final OutputStream HTMLOutstream)
+	protected void applyXSLTToHTML(final InputStream xmlFile, final OutputStream HTMLOutstream)
 			throws TransformerException {
 		Transformer transformer = mXsltHTMLTemplate.newTransformer();
 
 		transformer.transform(new StreamSource(xmlFile), new StreamResult(HTMLOutstream));
 	}
 
+	protected void applyXSLTToPDF(final InputStream xmlFile, final OutputStream PDFOutstream)
+			throws TransformerException {
+		Transformer transformer = mXsltPDFTemplate.newTransformer();
+
+		transformer.transform(new StreamSource(xmlFile), new StreamResult(PDFOutstream));
+	}
+
 	private static class ClasspathResourceURIResolver implements URIResolver {
 		ClasspathResourceURIResolver() {
 			// Do nothing, just prevents synthetic access warning.
@@ -212,7 +297,7 @@ public class ZUGFeRDVisualizer {
 
 		@Override
 		public Source resolve(String href, String base) throws TransformerException {
-			return new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH +"stylesheets/"+ href));
+			return new StreamSource(CLASS_LOADER.getResourceAsStream(RESOURCE_PATH + "stylesheets/" + href));
 		}
 	}
 }

library/src/test/java/org/mustangproject/ZUGFeRD/VisualizationTest.java

@@ -19,17 +19,23 @@
  *********************************************************************** */
 package org.mustangproject.ZUGFeRD;
 
+import org.apache.fop.apps.FOPException;
+import org.apache.fop.apps.FOUserAgent;
+import org.apache.fop.apps.Fop;
+import org.apache.fop.apps.FopFactory;
+import org.apache.xmlgraphics.util.MimeConstants;
 import org.junit.FixMethodOrder;
 import org.junit.runners.MethodSorters;
 import org.mustangproject.CII.CIIToUBL;
+import org.xml.sax.SAXException;
 
-import javax.xml.transform.TransformerException;
+import javax.xml.transform.*;
-import java.io.BufferedWriter;
+import javax.xml.transform.sax.SAXResult;
-import java.io.File;
+import javax.xml.transform.stream.StreamSource;
-import java.io.FileWriter;
+import java.io.*;
-import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
+import java.nio.file.Paths;
 
 @FixMethodOrder(MethodSorters.NAME_ASCENDING)
 public class VisualizationTest extends ResourceCase {
@@ -141,4 +147,91 @@ public class VisualizationTest extends ResourceCase {
 		// Reading ZUGFeRD
 		assertEquals(expected, result);
 	}
+
+	public void testPDFVisualization() {
+
+		// the writing part
+		CIIToUBL c2u = new CIIToUBL();
+		String sourceFilename = "factur-x.xml";
+		File CIIinputFile = getResourceAsFile(sourceFilename);
+
+		String expected = null;
+		String result = null;
+		try {
+			ZUGFeRDVisualizer zvi = new ZUGFeRDVisualizer();
+			/* remove file endings so that tests can also pass after checking
+			   out from git with arbitrary options (which may include CSRF changes)
+			 */
+			result = zvi.toFOP(CIIinputFile.getAbsolutePath());
+			File expectedResult=getResourceAsFile("fop.xml");
+			ByteArrayOutputStream fopout = new ByteArrayOutputStream();
+			//FileOutputStream outfile = new FileOutputStream("c:\\Users\\jstaerk\\temp\\fop2.pdf");
+		//	File out=new File("c:\\Users\\jstaerk\\temp\\fop.xml");
+
+// Step 1: Construct a FopFactory by specifying a reference to the configuration file
+// (reuse if you plan to render multiple documents!)
+			FopFactory fopFactory = FopFactory.newInstance(new File("c:\\Users\\jstaerk\\temp\\fop.xconf"));
+			FOUserAgent userAgent = fopFactory.newFOUserAgent();
+			userAgent.getRendererOptions().put("pdf-a-mode", "PDF/A-1b");
+
+// Step 2: Set up output stream.
+// Note: Using BufferedOutputStream for performance reasons (helpful with FileOutputStreams).
+			OutputStream out = new BufferedOutputStream(new FileOutputStream(new File("c:\\Users\\jstaerk\\temp\\fop3.pdf")));
+
+			try {
+				// Step 3: Construct fop with desired output format
+				Fop fop = fopFactory.newFop(MimeConstants.MIME_PDF, userAgent, out);
+
+				// Step 4: Setup JAXP using identity transformer
+				TransformerFactory factory = TransformerFactory.newInstance();
+				Transformer transformer = factory.newTransformer(); // identity transformer
+
+				// Step 5: Setup input and output for XSLT transformation
+				// Setup input stream
+				Source src = new StreamSource(new ByteArrayInputStream(result.getBytes(StandardCharsets.UTF_8)));
+
+				// Resulting SAX events (the generated FO) must be piped through to FOP
+				Result res = new SAXResult(fop.getDefaultHandler());
+
+				// Step 6: Start XSLT transformation and FOP processing
+				transformer.transform(src, res);
+
+				//Files.write(Paths.get("C:\\Users\\jstaerk\\temp\\fop.pdf"), res.toString().getBytes(StandardCharsets.UTF_8));
+
+			} finally {
+				//Clean-up
+				out.close();
+			}
+
+//			Fop fop = fopFactory.newFop(MimeConstants.MIME_PDF, fopout);
+/*
+			Transformer transformer = TransformerFactory.newInstance().newTransformer(
+					new StreamSource(new File(args[1])));
+			transformer.transform(new StreamSource(new File(args[0])),
+					new SAXResult(((Fop) fop).getDefaultHandler()));
+*/
+		//	fopout.toByteArray();
+
+			expected = new String(Files.readAllBytes(expectedResult.toPath()), StandardCharsets.UTF_8).replace("\r","").replace("\n","");
+			// remove linebreaks as well...
+
+		} catch (UnsupportedOperationException e) {
+			fail("UnsupportedOperationException should not happen: "+e.getMessage());
+		} catch (IllegalArgumentException e) {
+			fail("IllegalArgumentException should not happen: "+e.getMessage());
+		} catch (TransformerException e) {
+			fail("TransformerException should not happen: "+e.getMessage());
+		} catch (IOException e) {
+			fail("IOException should not happen: "+e.getMessage());
+		} catch (FOPException e) {
+			e.printStackTrace();
+		} catch (SAXException e) {
+			e.printStackTrace();
+		}
+
+		assertNotNull(result);
+		// Reading ZUGFeRD
+		assertEquals(expected, result);
+	}
+
 }