public static Set<PDFInfoHolder> getSimplePDFInfoHolders(File pdfs1, File pdfs2, String prefix)
	{
		Set<PDFInfoHolder> pdfInfoHolders = new HashSet<PDFInfoHolder>();
		
		// are those valid pathes
		if(pdfs1 != null && pdfs2 != null && pdfs1.isDirectory() && pdfs2.isDirectory())
		{
			// create a filter to only get pdf files
		    List<FilenameFilter> filters = new ArrayList<FilenameFilter>();
		    if (null != prefix && prefix.length() > 0 ) {
	            PrefixFileFilter filter = new PrefixFileFilter(prefix, IOCase.SYSTEM);
	            filters.add(filter);
		    }
		    filters.add(new SuffixFileFilter(".pdf", IOCase.INSENSITIVE));
            FilenameFilter filter = new AndFileFilter(filters);
            
			//get all pdf file sin this folder
			String[] pdfDocuments1 = pdfs1.list(filter);
			
			for (int i=0; i<pdfDocuments1.length; i++) 
			{	
				// get the pdf file name
			    String pdfFilename1 = pdfDocuments1[i];
			    
				// get the path for both pdf files
				File pdfFile1 = new File(pdfs1, pdfFilename1);
				File pdfFile2 = new File(pdfs2, pdfFilename1);
				
				// bind them together in a PDFInfoHolder objects
				PDFInfoHolder newPDFInfoHolder = new PDFInfoHolder(pdfFile1, pdfFile2);

				// remember them all
				pdfInfoHolders.add(newPDFInfoHolder);
			}
			
			// TODO what should happen if there are less reference documents than new generated ones
		}
		else
		{
			log.error("The path is not valid.");
		}		
		
		return pdfInfoHolders;
	}