Remove other operators and keep only Text operators(TJ,Tj) pdfBox

Question

I have a pdf from which I wish to remove all the image and other drawing content from it. and save the resultant as a new pdf.

I know how to remove text by using TJ , Tj operators , which I currently perform as below

op.getOperation().equals( "TJ")

Instead of removing the TJ,Tj operators , Is it possible to copy these Text operators onto an other pdf file with formatting intact so that the new pdf turns out to be pure text only pdf ? Its ok if text drawn using other than Tj , TJ operator misses out.

Code to remove TJ,Tj is taken from THIS stackoverflow post. But it partially works , it just removes images only, leaving drawing and other art intact.

EDIT : Other option I can think of is to set the cmyk color of all other operators outside the BT ET block to white. this way the pdf would feel text only. Is this possible ? If yes, Please support with code examples in pdfBox.

Answer 1

... THIS stackoverflow post. But it partially works , it just removes images only, leaving drawing and other art intact.

The main source of graphics other than bitmap graphics is vector graphics. They usually consist of path definitions followed by commands filling or stroking the path.

To remove these graphics you can improve the sample from the answer you referred to by additionally replacing those path striking or filling operators by the n operator which is a path-painting no-op.

            if( token instanceof PDFOperator )
            {
                PDFOperator op = (PDFOperator)token;
                if( op.getOperation().equals( "Do") )
                {
                    //remove the one argument to this operator
                    COSName name = (COSName)newTokens.remove( newTokens.size() -1 );
                    continue;
                }
                else if (PAINTING_PATH_OPS.contains(op.getOperation()))
                {
                    // replace path painting operator by path no-op
                    token = PDFOperator.getOperator("n");
                }
            }

where

final static List<String> PAINTING_PATH_OPS = Arrays.asList("S", "s", "F", "f", "f*", "B", "b", "B*", "b*");

contains the path striking or filling operators.

PS: The image removal code used in that referred-to answer has two drawbacks:

• It removes too much because it not only removes image xobjects but also form xobjects; sometimes (especially in n-up tool outputs) all content resides inside such form xobjects, including all text.

  To fix this you have to check the type of the referred-to xobject and only remove it if it has sub-type image. As form xobjects in turn can also contain images, you have to recurse into the form xobject (which has a content stream of its own).

• It removes too little because it ignores inlined images.

  To fix this you also have to look out for BI … Key-value pairs … ID … Image data … EI sections in the content and remove them.