closes #48

src/main/java/org/mustangproject/ZUGFeRD/ZUGFeRDImporter.java

@@ -61,6 +61,7 @@ public class ZUGFeRDImporter {
 	public void extract(String pdfFilename) {
 		try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(pdfFilename))) {
 			extractLowLevel(bis);
+			bis.close();
 		} catch (IOException ioe) {
 			ioe.printStackTrace();
 		}