diff --git a/validator/src/main/java/org/mustangproject/validator/ByteArraySearcher.java b/validator/src/main/java/org/mustangproject/validator/ByteArraySearcher.java
index ac1417c3..2cfc1514 100644
--- a/validator/src/main/java/org/mustangproject/validator/ByteArraySearcher.java
+++ b/validator/src/main/java/org/mustangproject/validator/ByteArraySearcher.java
@@ -34,4 +34,23 @@ public final class ByteArraySearcher {
 	public static boolean contains(byte[] haystack, byte[] needle) {
 	  return indexOf (haystack, needle) >= 0;
 	}
+
+  public static boolean startsWith(byte[] haystack, byte[] needle) {
+    if (needle.length > haystack.length) {
+      return false;
+    }
+    
+    // Any needle to search?
+    if (needle.length == 0) {
+      return false;
+    }
+
+    for (int j = 0; j < needle.length; j++) {
+      if (haystack[j] != needle[j]) {
+        return false;
+      }
+    }
+    
+    return true;
+  }
 }
diff --git a/validator/src/main/java/org/mustangproject/validator/PDFValidator.java b/validator/src/main/java/org/mustangproject/validator/PDFValidator.java
index b4b67ac9..47a5cb0d 100644
--- a/validator/src/main/java/org/mustangproject/validator/PDFValidator.java
+++ b/validator/src/main/java/org/mustangproject/validator/PDFValidator.java
@@ -5,6 +5,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.StringReader;
 import java.io.UnsupportedEncodingException;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.util.Arrays;
@@ -73,7 +74,7 @@ public class PDFValidator extends Validator {
 
 		zfXML = null;
 		// file existence must have been checked before
-		if (!ByteArraySearcher.contains(fileContents, new byte[]{'%', 'P', 'D', 'F'})) {
+		if (!ByteArraySearcher.startsWith(fileContents, new byte[]{'%', 'P', 'D', 'F'})) {
 			context.addResultItem(
 				new ValidationResultItem(ESeverity.fatal, "Not a PDF file " + pdfFilename).setSection(20).setPart(EPart.pdf));
 
@@ -254,37 +255,32 @@ public class PDFValidator extends Validator {
 		zfXML = zi.getUTF8();
 
 		// step 3 find signatures
-		try {
-			final byte[] symtraxSignature = "Symtrax".getBytes("UTF-8");
-			final byte[] mustangSignature = "via mustangproject".getBytes("UTF-8");
-			final byte[] facturxpythonSignature = "by Alexis de Lattre".getBytes("UTF-8");
-			final byte[] intarsysSignature = "intarsys ".getBytes("UTF-8");
-			final byte[] konikSignature = "Konik".getBytes("UTF-8");
-			final byte[] pdfMachineSignature = "pdfMachine from Broadgun Software".getBytes("UTF-8");
-			final byte[] ghostscriptSignature = "%%Invocation:".getBytes("UTF-8");
+		final byte[] symtraxSignature = "Symtrax".getBytes(StandardCharsets.UTF_8);
+		final byte[] mustangSignature = "via mustangproject".getBytes(StandardCharsets.UTF_8);
+		final byte[] facturxpythonSignature = "by Alexis de Lattre".getBytes(StandardCharsets.UTF_8);
+		final byte[] intarsysSignature = "intarsys ".getBytes(StandardCharsets.UTF_8);
+		final byte[] konikSignature = "Konik".getBytes(StandardCharsets.UTF_8);
+		final byte[] pdfMachineSignature = "pdfMachine from Broadgun Software".getBytes(StandardCharsets.UTF_8);
+		final byte[] ghostscriptSignature = "%%Invocation:".getBytes(StandardCharsets.UTF_8);
 
-			if (ByteArraySearcher.contains(fileContents, symtraxSignature)) {
-				Signature = "Symtrax";
-			} else if (ByteArraySearcher.contains(fileContents, mustangSignature)) {
-				Signature = "Mustang";
-			} else if (ByteArraySearcher.contains(fileContents, facturxpythonSignature)) {
-				Signature = "Factur/X Python";
-			} else if (ByteArraySearcher.contains(fileContents, intarsysSignature)) {
-				Signature = "Intarsys";
-			} else if (ByteArraySearcher.contains(fileContents, konikSignature)) {
-				Signature = "Konik";
-			} else if (ByteArraySearcher.contains(fileContents, pdfMachineSignature)) {
-				Signature = "pdfMachine";
-			} else if (ByteArraySearcher.contains(fileContents, ghostscriptSignature)) {
-				Signature = "Ghostscript";
-			}
-
-			context.setSignature(Signature);
-
-		} catch (final UnsupportedEncodingException e) {
-			LOGGER.error(e.getMessage(), e);
+		if (ByteArraySearcher.contains(fileContents, symtraxSignature)) {
+			Signature = "Symtrax";
+		} else if (ByteArraySearcher.contains(fileContents, mustangSignature)) {
+			Signature = "Mustang";
+		} else if (ByteArraySearcher.contains(fileContents, facturxpythonSignature)) {
+			Signature = "Factur/X Python";
+		} else if (ByteArraySearcher.contains(fileContents, intarsysSignature)) {
+			Signature = "Intarsys";
+		} else if (ByteArraySearcher.contains(fileContents, konikSignature)) {
+			Signature = "Konik";
+		} else if (ByteArraySearcher.contains(fileContents, pdfMachineSignature)) {
+			Signature = "pdfMachine";
+		} else if (ByteArraySearcher.contains(fileContents, ghostscriptSignature)) {
+			Signature = "Ghostscript";
 		}
 
+		context.setSignature(Signature);
+
 		// step 4:validate additional data
 		final HashMap<String, byte[]> additionalData = zi.getAdditionalData();
 		for (final String filename : additionalData.keySet()) {
diff --git a/validator/src/main/java/org/mustangproject/validator/ZUGFeRDValidator.java b/validator/src/main/java/org/mustangproject/validator/ZUGFeRDValidator.java
index 38874cfd..64fc8c4b 100644
--- a/validator/src/main/java/org/mustangproject/validator/ZUGFeRDValidator.java
+++ b/validator/src/main/java/org/mustangproject/validator/ZUGFeRDValidator.java
@@ -114,7 +114,7 @@ public class ZUGFeRDValidator {
         if (disableNotices) {
           xv.disableNotices();
         }
-        isPDF = ByteArraySearcher.indexOf(content, new byte[] {'%', 'P', 'D', 'F'}) == 0;
+        isPDF = ByteArraySearcher.startsWith(content, new byte[] {'%', 'P', 'D', 'F'});
         if (isPDF) {
           // Avoid reading again from file
           pdfv.setFilenameAndContents(contextFilename, content);
diff --git a/validator/src/test/java/org/mustangproject/validator/ByteArraySearcherTest.java b/validator/src/test/java/org/mustangproject/validator/ByteArraySearcherTest.java
index e658a085..9d660c67 100644
--- a/validator/src/test/java/org/mustangproject/validator/ByteArraySearcherTest.java
+++ b/validator/src/test/java/org/mustangproject/validator/ByteArraySearcherTest.java
@@ -1,24 +1,42 @@
 package org.mustangproject.validator;
 
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import java.nio.charset.StandardCharsets;
 
 import org.junit.Test;
 
-public class ByteArraySearcherTest {
+public class ByteArraySearcherTest
+{
   @Test
   public void testIndexOf () {
-    byte[] haystack = "Hello World".getBytes (StandardCharsets.ISO_8859_1);
-    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte[] {'H'}));
-    assertEquals (1, ByteArraySearcher.indexOf (haystack, new byte[] {'e'}));
-    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte[] {'H', 'e'}));
-    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte[] {'H', 'e'}));
-    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte[] {'H', 'e', 'l', 'l'}));
+    byte [] haystack = "Hello World".getBytes (StandardCharsets.ISO_8859_1);
+    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte [] { 'H' }));
+    assertEquals (1, ByteArraySearcher.indexOf (haystack, new byte [] { 'e' }));
+    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte [] { 'H', 'e' }));
+    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte [] { 'H', 'e' }));
+    assertEquals (0, ByteArraySearcher.indexOf (haystack, new byte [] { 'H', 'e', 'l', 'l' }));
     assertEquals (0, ByteArraySearcher.indexOf (haystack, haystack));
-    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte[0]));
-    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte[] {'a'}));
-    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte[] {'h'}));
-    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte[] {'r', 'o'}));
+    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte [0]));
+    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte [] { 'a' }));
+    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte [] { 'h' }));
+    assertEquals (-1, ByteArraySearcher.indexOf (haystack, new byte [] { 'r', 'o' }));
+  }
+
+  @Test
+  public void testStartsWith () {
+    byte [] haystack = "Hello World".getBytes (StandardCharsets.ISO_8859_1);
+    assertTrue (ByteArraySearcher.startsWith (haystack, new byte [] { 'H' }));
+    assertFalse (ByteArraySearcher.startsWith (haystack, new byte [] { 'e' }));
+    assertTrue (ByteArraySearcher.startsWith (haystack, new byte [] { 'H', 'e' }));
+    assertTrue (ByteArraySearcher.startsWith (haystack, new byte [] { 'H', 'e' }));
+    assertTrue (ByteArraySearcher.startsWith (haystack, new byte [] { 'H', 'e', 'l', 'l' }));
+    assertTrue (ByteArraySearcher.startsWith (haystack, haystack));
+    assertFalse (ByteArraySearcher.startsWith (haystack, new byte [0]));
+    assertFalse (ByteArraySearcher.startsWith (haystack, new byte [] { 'a' }));
+    assertFalse (ByteArraySearcher.startsWith (haystack, new byte [] { 'h' }));
+    assertFalse (ByteArraySearcher.startsWith (haystack, new byte [] { 'r', 'o' }));
   }
 }