(The main tools used to generate PDF files are Adobe's Acrobat Distiller, PDFLib open source library, and some virtual printer tools that can generate PDF results. These tools have more or less minor problems in the process of generating PDF files. When Acrobat Distiller makes PDF files, it does not use the higher compression rate JBIG2 encoding for black and white images, but uses CCITTFax encoding; when using PDFLib to make PDF files, sometimes many useless objects are generated in the file.)