Adjust the output by defining sections of PDFs.

It's possible to convert a specific page, but sometimes we only want to convert a specific portion of the PDF (a graphic, a bunch of text, etc.), so it would be useful if PDF Converter would allow us to define a section (even the same section in all pages) for being converted.

This is particularly handy when we convert PDFs with headers and page breaks to text: In the traditional way, the output file is partially unreadable and requires an extra work of deleting the header text converted. With an option of "croping" the conversion, the output file will only get the data we need.