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Search text in PDF documents (C# sample)

While building the perfect apps with Apitron PDF Rasterizer for .NET you were probably thinking about own PDF text search functionality implementation.
It could be useful for custom viewers, and having this feature makes your PDF rendering toolkit really complete: you’d have the Apitron PDFRasterizer for rendering, Apitron PDF Viewer (our free pdf viewer control) for viewing and integrated text search for fast and efficient text search and navigation.
We did it for you.
From now on, the Apitron PDF Rasterizer has the integrated text search engine and you can easily use it in your apps.

The code 

For demonstration purposes we will review a sample that opens PDF file, searches for some text, renders corresponding PDF page and highlights the results(complete C# code can be found under samples\SearchAndHighlightSpecifiedText folder in our download package).

Our PDF text search engine uses concept called search index, prior to searching we analyze the document and build its “index” - data used for actual searching. It can be stored by you for later use if you wish, so you could avoid its recreation next time the document is being opened.

Index creation

FileStream pdfDocumentStreamToSearch = new FileStream( Path.Combine( pathToDocuments, "2003_ar.pdf" ), FileMode.Open, FileAccess.Read );

SearchIndex searchIndex = new SearchIndex( pdfDocumentStreamToSearch );

As you see, index creation takes just a few lines of code. It’s also possible to save the index to output stream for later use. Password-protected PDF files are also supported.

Text search 

I used the PDF document from Adobe website, http://www.adobe.com/aboutadobe/invrelations/pdfs/2003_ar.pdf and all images attached to this post represent actual output from the code sample.

static void Main(string[] args)
   string pathToDocument = @"..\Documents\2003_ar.pdf";

   // create index from PDF file
   using ( Stream pdfDocumentStreamToSearch = new FileStream( pathToDocument, FileMode.Open, FileAccess.Read ) )
      SearchIndex searchIndex = new SearchIndex(pdfDocumentStreamToSearch);

      // create document used for rendering
      using ( Stream pdfDocumentStreamToRasterize = new FileStream( pathToDocument, FileMode.Open, FileAccess.Read ) )
         document = new Document(pdfDocumentStreamToRasterize);
         // search text in PDF document and render pages containing results
         searchIndex.Search( SearchHandler, "software products derive" );

/// <summary>
/// Handle search results here. Draw pages with highlighted text.
/// </summary>
/// <param name="handlerArgs">The handler args.</param>
private static void SearchHandler(SearchHandlerArgs handlerArgs)
   if (handlerArgs.ResultItems.Count != 0)
      string outputFileName = string.Format("{0}.png", handlerArgs.PageIndex);
      Page page = document.Pages[handlerArgs.PageIndex];
      using (Image bm = page.Render((int)page.Width * 2, (int)page.Height * 2, renderingSettings))
         foreach (SearchResultItem searchResultItem in handlerArgs.ResultItems)
            HighlightSearchResult(bm, searchResultItem, page);

         bm.Save( outputFileName );

      Process.Start( outputFileName );

   // Search cancellation condition, now we stop if we have more than 3 results found,
   // or all pages are searched
   if (handlerArgs.ResultItems.Count > 3)
      handlerArgs.CancelSearch = true;


What happens here? We take the previously created index data and call the SearchIndex.Search method accepting the search event handler.
It processes our results one by one and highlights found items using HighlightSearchResult call - this method contains simple GDI+ code that draws a transparent rectangle around the found text (if any). It also has a condition set for search cancellation, demonstrating the flexibility of PDF search API.

Resulting images

Resulting image(see yellow markers)

One of the results produced by searching for “Intelligent Documents”

Result produced for spiral text

How to get it 

The described PDF search engine is included in latest Apitron PDF Rasterizer for .NET release, all related classes can be found under Apitron.PDF.Rasterizer.Search namespace. We always welcome any feedback, so feel free to ask questions and share ideas.


  1. Hello, how to search text with Windows phone version?

  2. Hi, you may use the same code and API for it.

  3. Hi!!.. You already confirm me that we could save for later use in database (sql server) searchIndex variable. We still hasn't start to implement this, but to advance I will like to know if we should use Long Text for example.

    Also, do you think that saving index in DB will save us some resources (it's a web application)? In this way we wouldn't have to call SearchFunction everytime a user search in PDF.


    1. Hello Ricardo,
      yes it's possible, it can speed up text search significantly. It seems that BLOB/ FILESTREAM suits better for the index data than long text.

  4. Hi, I have used Apitron dll for searching but I am getting result up to 3 pages only. Is there any restriction for searching or am I doing any thing wrong? Please guide me.

    1. Hello Anuj, yes it's the evaluation limitation.

  5. Hi
    I have following scenario kindly help/guide me urgently
    I have thousands of pdf's that i want to upload on webserver.
    Now that will be available as public site where hundred of thousands of people can search pdf at a time.
    I am developing asp.net application
    Kindly guide me your recommendation how to implement this thing in above scenario.

    1. Please contact our support and we'll discuss your case.