* @return PdfFile array from the input directory
*/
protected PdfFile[] getPdfFiles(final File directory) {
PdfFile[] retVal = null;
if (directory != null && directory.isDirectory()) {
File[] fileList = directory.listFiles(new PdfFilter());
Arrays.sort(fileList, new FilenameComparator());
ArrayList list = new ArrayList();
for (int i = 0; i < fileList.length; i++) {
list.add(new PdfFile(fileList[i], null));
}