How to insert invisible text into PDF?

Question

I want to insert invisible text into an existing PDF file to make it searchable.

Which library should I use?
I would like to get links to specific API methods .

Free, perfectly open source.
Many thanks!

(For the curious: I want to automatically record incoming scanned documents and make them scanned in the Alfresco repository)

Answer 1

3 options.

• Text visualization mode 3: "No stroke, no fill." myPdfContentByte.setTextRenderMode(PdfContentByte.TEXT_RENDER_MODE_INVISIBLE);
• -. . iText myPdfStamper.getUnderContent(pageNum) .
• . , - PDF-savvy , , , , PDF, ... .

Answer 2

, PDF, , this , . , - "" , . .

Answer 3

You do not need to display the text invisible. Just put them in the right place, but overlay the scanned image on the text. Or you can make the text above the image and set the alpha value of the color of the stroke and brush to zero.