PDFNet.Initialize();
ArrayList rarr = new ArrayList();
rarr.Add(new Redactor.Redaction(1, new Rect(0, 0, 600, 600), true, "Top Secret"));
rarr.Add(new Redactor.Redaction(2, new Rect(30, 30, 550, 550), true, "Top Secret"));
using (PDFDoc doc = new PDFDoc("confidential.pdf")) {
doc.InitSecurityHandler();
Redactor.Appearance app = new Redactor.Appearance();
app.Font = new System.Drawing.Font("Arial", 12);
app.PositiveOverlayColor = System.Drawing.Color.Red;
app.NegativeOverlayColor = System.Drawing.Color.WhiteSmoke;
Redactor.Redact(doc, rarr, app);
doc.Save("redacted.pdf", SDFDoc.SaveOptions.e_linearized);
}
----
So to redact a PDF you just pass a collection of rectangles to 'Redactor.Redact'.
Now to let the user interactively define redaction regions (i.e. draw rects on content) you can use either the native PDF viewer control that comes as part of PDFNet SDK (e.g. PDFView sample) or you can use the WebViewer.
In either case you would either create a custom annotation tool ... or perhaps you can simply use built-in annotation tool (so no extra work required). In case you need a custom annotation tool as a desktop app MyPDFView.cs in PDFNet SDK. In case of WebViewer see Annotation related APIs (http://www.pdftron.com/pdfnet/webviewer/demo/html5/doc/index.html) and in case you wont to write a custom annotation ('WebViewer\html5\AnnotationNotes.txt'). In any case, I would just recommend using built-in rectangle annotations which can be exported to XML string via 'CoreControls.AnnotationManager SaveAnnotations()'. You would then send the XML string to server where you can load XFDF to FDFDoc (see http://www.pdftron.com/pdfnet/samplecode/FDFTest.cs) extract the list of annotation rectangles and pass them to 'Redactor.Redact'.
For a relevant post please see:
[WebViewer] PDF / XPS redaction in a web browser:
https://groups.google.com/d/topic/pdfnet-webviewer/jKtzGvbmNpU/discussion
Regarding licensing you should probably apply for it after you sort out technical things (e.g. what exactly component services you need). When you are ready please fill out http://www.pdftron.com/store/oem.htmlwith detailed information and our sales will get back to you with a proposal.