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Home » Newsletter » February 2012

By V. Subhash

In Version 4 of PDFOne .NET, we have introduced methods to implement PDF text search.

public ArrayList Search(
   // search string
   string searchString,
   // page number
   int pageNum,
   // literal or regular expression
   PDFSearchMode searchMode,
   // generous-match, case-sensitive, whole-word
   PDFSearchOptions searchOptions
)

public ArrayList Search(
   // search begins from
   int startPageNum,
   string searchString,
   PDFSearchMode searchMode,
   PDFSearchOptions searchOptions
)

public void Search(
   string searchString,
   PDFSearchMode searchMode,
   PDFSearchOptions searchOptions,
   // event handler to be called when a match is found
   SearchElementHandler pdfSearchHandler,
   int startPageNum
)

The first two overloads return an array list containing the lines that were extracted. The third overload does not return anything. Instead, it calls the specified event handler whenever it finds a match. Inside the event handler, you will be able to access the search results from the parameters.

These methods enable you to perform simple text searches using literal strings and advanced text searches using regular expressions.

Simple Text Search

The following code snippet illustrates the former.

PDFDocument PDFDocument1 = new PDFDocument("your-license-key");

// Load PDF document
PDFDocument1.Load("sample_doc.pdf");

// Obtain all instances of the word "bike" in page 4
ArrayList ArrayList1 =
      (ArrayList) PDFDocument1.Search("bike",
                                      1,
                                      PDFSearchMode.LITERAL,
                                      PDFSearchOptions.NONE);
// Close the document
PDFDocument1.Close();

// Iterate through all search results
PDFSearchElement PdfSearchElement1;
int n = ArrayList1.Count;
for (int i = 0; i < n; i++) {
  PdfSearchElement1 = (PDFSearchElement) ArrayList1[i];
  // Print search results to console output
  Console.WriteLine("Found \"" +
                         PdfSearchElement1.MatchString +
                         "\" in page #" +
                         PdfSearchElement1.PageNumber +
                         " text \"" +
                         PdfSearchElement1.LineContainingMatchString +
                         "\"" );
}

// Close the document
PDFDocument1.Close();
Console.ReadLine();

Here is the document we used for testing this code.

And, here is the output.

Advanced PDF Text Search

Regular expressions are performance-multipliers. Using cleverly crafted regular expressions, you can eliminate several lines from you code. All the search() methods support regular expressions. The following code snippet shows how to use them.

PDFDocument PDFDocument1 = new PDFDocument("your-license-key");

// Load PDF document
PDFDocument1.Load("sample_.pdf");


// Obtain all hyperlinks in page 2
ArrayList ArrayList1 =
      (ArrayList)PDFDocument1.Search(@"http://{1}",
                                      2,
                                      PDFSearchMode.REGEX,
                                      PDFSearchOptions.NONE);
// Close the document
PDFDocument1.Close();

// Iterate through all search results
PDFSearchElement PdfSearchElement1;
int n = ArrayList1.Count;
for (int i = 0; i < n; i++) {
  PdfSearchElement1 = (PDFSearchElement) ArrayList1[i];
  // Print search results to console output
  Console.WriteLine("Found \"" +
                         PdfSearchElement1.MatchString +
                         "\" in page #" +
                         PdfSearchElement1.PageNumber +
                         " text \"" +
                         PdfSearchElement1.LineContainingMatchString +
                         "\"" );
}

// Close the document
PDFDocument1.Close();
Console.ReadLine();

The above code snippet uses a simple regular expression that matches web page links. To test this code snippet, we used the following document.

And, here is the output. Note how all the hyperlinks have been neatly caught by the search.

PDF Text Extraction

The search methods find text in the order it is available in the document. This may not always be in the order that a human reads a page - from top to bottom. If you want it all ordered, then you should first extract all text from the page and then search the extracted text. The following code snippet shows how to extract all text content from a PDF page.

// Create a PDF document object
PDFDocument PDFDocument1 = new PDFDocument("your-license-key");

// Load PDF document
PDFDocument1.Load("sample_doc.pdf");

// Extract text from page 1
ArrayList aExtractedText = PDFDocument1.ExtractText(1);

// Save extracted text to file
using (StreamWriter StreamWriter1 = File.CreateText("extracted_content.txt"))  {
  foreach (string sLine in aExtractedText) {
    StreamWriter1.Write(sLine);
  }

StreamWriter1.Close();

We tested this code snippet on a PDF document containing the license agreement of one of our products. Here is that document and the extracted text.