Q: We are looking for a .NET library for generating and comparing PDF documents.
We need to compare an “original” and a “revised” PDF document and show the differences between them. Ideally the library would be accessed by a web service we establish and would deliver a PDF of the highlighted changes back to the client. We are not looking for any UI components as these features would need to be fully integrated into another application.
For comparison, you would probably use pdftron.PDF.PDFDraw.GetBitmap() as shown in PDFDraw sample:
Once you have images you can compare them with image diff utility (e.g. http://pdiff.sourceforge.net/, image magic, opencv, etc).
You can add highlights on existing PDF pages using ‘pdftron.PDF.Stamper’ (http://www.pdftron.com/pdfnet/samplecode.html#Stamper) or ElementBuilder/ElementWriter (see ‘How do I add a watermark to a page?’ in http://www.pdftron.com/pdfnet/faq.html). The later option offers more flexibility at the expense of extra coding.