This handler can be used to handle conversion progress events f.e. it can be used to show progress bar or messages about current amount of processed pages, example of handler's code that shows progress on console is :

Sometimes PDFs contain background images (of pages or table cells) constructed from several same tiling background images put one near other. In such case renderers of target formats (f.e MsWord for DOCS format) sometimes generates visible boundaries beetween parts of background images, cause their techniques of image edge smoothing (anti-aliasing) is different from Acrobat Reader. If it looks like exported document contains such visible boundaries between parts of same background images, please try use this setting to get rid of that unwanted effect. ATTENTION! This optimization of quality usually essentially slows down conversion, so, please, use this option only when it's really necessary.