How can I Extract words with its coordinates from pdf using .net?

Question

I'm working with pdf in hebrew language with diacritical marks. I want to extract all the words with its coordinates. I tried to use ITextSharp and pdfClown and they both didn't give me what I want.

In pdfClown there are missing letters\chars in ITextSharp I don't get the words coordinates.

Is there a way to do it? (I'm looking for a free framework\code)

EDIT:

PDFClown Code:

    File file = new File(PDFFilePath);
    TextExtractor te = new TextExtractor();
    IDictionary<RectangleF?, IList<ITextString>> strs = te.Extract(file.Document.Pages[0].Contents);

    List<string> correctText = new List<string>();
    foreach (var key in strs.Keys)
    {
        foreach (var value in strs[key])
        {
            string reversedText = new string(value.Text.Reverse().ToArray());
            string cleanText = RemoveDiacritics(reversedText);
            correctText.Add(cleanText);
        }
    }

Answer 1

You aren't showing how you are trying to extract text using iText(Sharp). I am assuming that you are following the official documentation and that your code looks like this:

public string ExtractText(byte[] src) {
    PdfReader reader = new PdfReader(src);
    MyTextRenderListener listener = new MyTextRenderListener();
    PdfContentStreamProcessor processor = new PdfContentStreamProcessor(listener);
    PdfDictionary pageDic = reader.GetPageN(1);
    PdfDictionary resourcesDic = pageDic.GetAsDict(PdfName.RESOURCES);
    processor.ProcessContent(
       ContentByteUtils.GetContentBytesForPage(reader, 1), resourcesDic);
    return listener.Text.ToString();
}

If your code doesn't look like this, this explains already explains the first thing you're doing wrong.

In this method, there is one class that isn't part of iTextSharp: MyTextRenderListener. This is a class you should write and that looks for instance like this:

public class MyTextRenderListener : IRenderListener {
    public StringBuilder Text { get; set; }

    public MyTextRenderListener() {
        Text = new StringBuilder();
    }
    public void BeginTextBlock() {
        Text.Append("<");
    }
    public void EndTextBlock() {
        Text.AppendLine(">");
    }
    public void RenderImage(ImageRenderInfo renderInfo) {
    }
    public void RenderText(TextRenderInfo renderInfo) {
        Text.Append("<");
        Text.Append(renderInfo.GetText());
        LineSegment segment = renderInfo.GetBaseline();
        Vector start = segment.GetStartPoint();
        Text.Append("| x=");
        Text.Append(start[Vector.I1]);
        Text.Append("; y=");
        Text.Append(start[Vector.I2]);
        Text.Append(">");
    }    
}

When you run this code, and you look what's inside Text, you'll notice that a PDF document doesn't store words. Instead, it stores text blocks. In our special IRenderListener, we indicate the start and the end of text blocks using < and >. Inside these text blocks, you'll find text snippets. We'll mark text snippets like this: <text snippet| x=36.0000; y=806.0000> where the x and y value give you the coordinate of the start of the baseline (as opposed to the ascent and descent position). You can also get the end position of the baseline (and the ascent/descent).

Now how do you distill words out of all of this? The problem with the text snippets you get, is that they don't correspond with words. See for instance this file: hello_reverse.pdf

When you open it in Adobe Reader, you read "Hello World Hello People." You'd hope you'd find four words in the content stream, wouldn't you? In reality, this is what you'll find:

<>
<<ld><Wor><llo><He>>
<<Hello People>>

To distill the words, "World" and "Hello" from the first line, you need to do plenty of Math. Instead of getting the base line of the TextRenderInfo object returned in the RenderText() method of your render listener, you have to use the GetCharacterRenderInfos() method. This will return a list of TextRenderInfo objects that gives you more info about every character (including the position of those characters). You then need to compose the words from those different characters.

This is explained in mkl's answer to this question: Retrieve the respective coordinates of all words on the page with itextsharp

We've done similar projects. One of them is described here: https://www.youtube.com/watch?v=lZnbhnU4m3Y

You'll need to do quite some coding to get it right. One word about PdfClown: your text is probably stored as UNICODE in your PDF. To retrieve the correct characters, the parser needs to examine the mapping of the glyphs stored in the font and the corresponding UNICODE character. If PdfClown can't do this, this means that PdfClown doesn't do this task correctly. PdfClown is a one man project, so you'll have to ask that developer to fix this (if he has the time).

As you can tell from the video, iText could help you out, but iText is a company with subsidiaries in the US, Belgium and Singapore. It is a company with many employees and to keep that company running, we need to make money (that's how we pay our employees). Hence you shouldn't expect that we help you for free. Surely you can understand this as you wouldn't want to work for free either, would you?