iText - add content to existing PDF file

iText has more than one way of doing this. The PdfStamper class is one option. But I find the easiest method is to create a new PDF document then import individual pages from the existing document into the new PDF.

// Create output PDF
Document document = new Document(PageSize.A4);
PdfWriter writer = PdfWriter.getInstance(document, outputStream);
document.open();
PdfContentByte cb = writer.getDirectContent();

// Load existing PDF
PdfReader reader = new PdfReader(templateInputStream);
PdfImportedPage page = writer.getImportedPage(reader, 1); 

// Copy first page of existing PDF into output PDF
document.newPage();
cb.addTemplate(page, 0, 0);

// Add your new data / text here
// for example...
document.add(new Paragraph("my timestamp")); 

document.close();

This will read in a PDF from templateInputStream and write it out to outputStream. These might be file streams or memory streams or whatever suits your application.

Gutch's code is close, but it'll only work right if:

• There are no annotations (links, fields, etc), no Document Structure/Marked Content, no bookmarks, no document-level script, etc, etc, etc...
• The page size happens to be A.4 (decent odds, but it won't work on any ol' PDF you happen to come across)
• You don't mind losing all the original document metadata (producer, creation date, possibly author/title/keywords), and maybe the document ID. You can't copy the creation date and doc ID unless you do some pretty deep hackery on iText itself).

The Approved Method is to do it the other way around. Open the existing document with a PdfStamper, and use the returned PdfContentByte from getOverContent() to write text (and whatever else you might need) directly to the page. No second document needed.

And you can use a ColumnText to handle layout and such for you... no need to get down and dirty with beginText(),setFontAndSize(),drawText(),drawText()...,endText().