Q: We need to present PDF documents in editable format to the end users through our website. Users should be allowed to edit/add Text within the PDF (Images and format does not change). The users should be allowed to edit PDF document or maybe HTML presented to them but this should reflect in the original PDF after editing which can be then printed if required. The format of original PDF should not change.
Converting a PDF to an editable document that retains the formatting of the original is not generally possible. This is because PDF is a fixed document format, best thought of as a printed page, which does not generally include structural information such as which letters form words, lines, paragraphs, etc. Additionally, fonts may be subsetted so that unless a particular letter is used in the PDF, it cannot be added elsewhere.
If it is acceptable for your solution, you could convert a PDF to HTML, and then HTML back to PDF, but the resultant PDF will be unlikely to “look the same” as the original. Please let me know if you would like further details about this approach.
In case you only need to allow editing through markup and annotations (e.g. sticky notes, hilites, etc) you could use SilverDox (http://www.pdftron.com/silverdox/samplecode.html) or PDFNet WebViewer (http://www.pdftron.com/pdfnet/webviewer/demo.html) both of which come with a customizable annotation API.