Comparison of two pdf files

Question

I need to compare the contents of two almost similar files and highlight the dissimilar portions in the corresponding pdf file. Am using pdfbox. Please help me atleast with

Answer 1

If you prefer a tool with a GUI, you could try this one: diffpdf. It's by Mark Summerfield, and since it's written with Qt, it should be available (or should be buildable) on all platforms where Qt runs on.

Here's a screenshot:

Answer 2

I had this very problem myself and the quickest way that I've found is to use PHP and its bindings for ImageMagick (Imagick).

<?php
$im1 = new \Imagick("file1.pdf");
$im2 = new \Imagick("file2.pdf");

$result = $im1->compareImages($im2, \Imagick::METRIC_MEANSQUAREERROR);

if($result[1] > 0.0){
    // Files are DIFFERENT
}
else{
    // Files are IDENTICAL
}

$im1->destroy();
$im2->destroy();

Of course, you need to install the ImageMagick bindings first:

sudo apt-get install php5-imagick # Ubuntu/Debian

Answer 3

You can do the same thing with a shell script on Linux. The script wraps 3 components:

1. ImageMagick's compare command
2. the pdftk utility
3. Ghostscript

It's rather easy to translate this into a .bat Batch file for DOS/Windows...

Here are the building blocks:

pdftk

Use this command to split multipage PDF files into multiple singlepage PDFs:

pdftk  first.pdf  burst  output  somewhere/firstpdf_page_%03d.pdf
pdftk  2nd.pdf    burst  output  somewhere/2ndpdf_page_%03d.pdf

compare

Use this command to create a "diff" PDF page for each of the pages:

compare \
       -verbose \
       -debug coder -log "%u %m:%l %e" \
        somewhere/firstpdf_page_001.pdf \
        somewhere/2ndpdf_page_001.pdf \
       -compose src \
        somewhereelse/diff_page_001.pdf

Note, that compare is part of ImageMagick. But for PDF processing it needs Ghostscript as a 'delegate', because it cannot do so natively itself.

Once more, pdftk

Now you can again concatenate your "diff" PDF pages with pdftk:

pdftk \
      somewhereelse/diff_page_*.pdf \
      cat \
      output somewhereelse/diff_allpages.pdf

Ghostscript

Ghostscript automatically inserts meta data (such as the current date+time) into its PDF output. Therefore this is not working well for MD5hash-based file comparisons.

If you want to automatically discover all cases which consist of purely white pages (that means: there are no visible differences in your input pages), you could also convert to a meta-data free bitmap format using the bmp256 output device. You can do that for the original PDFs (first.pdf and 2nd.pdf), or for the diff-PDF pages:

 gs \
   -o diff_page_001.bmp \
   -r72 \
   -g595x842 \
   -sDEVICE=bmp256 \
    diff_page_001.pdf

 md5sum diff_page_001.bmp

Just create an all-white BMP page with its MD5sum (for reference) like this:

 gs \
   -o reference-white-page.bmp \
   -r72 \
   -g595x842 \
   -sDEVICE=bmp256 \
   -c "showpage quit"

 md5sum reference-white-page.bmp

Answer 4

I have come up with a jar using apache pdfbox to compare pdf files - this can compare pixel by pixel & highlight the differences.

Check my blog : http://www.testautomationguru.com/introducing-pdfutil-to-compare-pdf-files-extract-resources/ for example & download.

---

To get page count

import com.taguru.utility.PDFUtil;

PDFUtil pdfUtil = new PDFUtil();
pdfUtil.getPageCount("c:/sample.pdf"); //returns the page count

To get page content as plain text

//returns the pdf content - all pages
pdfUtil.getText("c:/sample.pdf");

// returns the pdf content from page number 2
pdfUtil.getText("c:/sample.pdf",2);

// returns the pdf content from page number 5 to 8
pdfUtil.getText("c:/sample.pdf", 5, 8);

To extract attached images from PDF

//set the path where we need to store the images
 pdfUtil.setImageDestinationPath("c:/imgpath");
 pdfUtil.extractImages("c:/sample.pdf");

// extracts & saves the pdf content from page number 3
pdfUtil.extractImages("c:/sample.pdf", 3);

// extracts & saves the pdf content from page 2
pdfUtil.extractImages("c:/sample.pdf", 2, 2);

To store PDF pages as images

//set the path where we need to store the images
 pdfUtil.setImageDestinationPath("c:/imgpath");
 pdfUtil.savePdfAsImage("c:/sample.pdf");

To compare PDF files in text mode (faster – But it does not compare the format, images etc in the PDF)

String file1="c:/files/doc1.pdf";
String file1="c:/files/doc2.pdf";

// compares the pdf documents & returns a boolean
// true if both files have same content. false otherwise.
pdfUtil.comparePdfFilesTextMode(file1, file2);

// compare the 3rd page alone
pdfUtil.comparePdfFilesTextMode(file1, file2, 3, 3);

// compare the pages from 1 to 5
pdfUtil.comparePdfFilesTextMode(file1, file2, 1, 5);

To compare PDF files in Binary mode (slower – compares PDF documents pixel by pixel – highlights pdf difference & store the result as image)

String file1="c:/files/doc1.pdf";
String file1="c:/files/doc2.pdf";

// compares the pdf documents & returns a boolean
// true if both files have same content. false otherwise.
pdfUtil.comparePdfFilesBinaryMode(file1, file2);

// compare the 3rd page alone
pdfUtil.comparePdfFilesBinaryMode(file1, file2, 3, 3);

// compare the pages from 1 to 5
pdfUtil.comparePdfFilesBinaryMode(file1, file2, 1, 5);

//if you need to store the result
pdfUtil.highlightPdfDifference(true);
pdfUtil.setImageDestinationPath("c:/imgpath");
pdfUtil.comparePdfFilesBinaryMode(file1, file2);