How to update a PDF file? - asp.net

Question

I am required to replace a word with a new word, selected from a drop-down list by user, in a PDF document in ASP.NET. I am using iTextSharp , but the new PDF that is created is all distorted as I am not able to extract the formatting/styling info of the PDF while extracting. Also, IS There a way to read a pdf line-by-line? Please help..
protected void Page_Load(object sender, EventArgs e)
{
String s = DropDownList1.SelectedValue;
Response.Write(s);
ListFieldNames(s);
}
private void CreatePDF(string text)
{
string outFileName = #"z:\TEMP\PDF\Test_abc.pdf";
Document doc = new Document();
doc.SetMargins(30f, 30f, 30f, 30f);
PdfWriter.GetInstance(doc, new FileStream(outFileName, FileMode.Create));
doc.Open();
BaseFont bfTimes = BaseFont.CreateFont(BaseFont.COURIER, BaseFont.CP1252, false);
Font times = new Font(bfTimes, 12, Font.BOLDITALIC);
//Chunk ch = new Chunk(text,times);
Paragraph para = new Paragraph(text,times);
//para.SpacingAfter = 9f;
para.Alignment = Element.ALIGN_CENTER;
//para.IndentationLeft = 100;
doc.Add(para);
//doc.Add(new Paragraph(text,times));
doc.Close();
Response.Redirect(#"z:\TEMP\PDF\Test_abc.pdf",false);
}
private void ListFieldNames(string s)
{
ArrayList arrCheck = new ArrayList();
try
{
string pdfTemplate = #"z:\TEMP\PDF\abc.pdf";
//string dest = #"z:\TEMP\PDF\Test_abc.pdf";
PdfReader pdfReader = new PdfReader(pdfTemplate);
string pdfText = string.Empty;
string extracttext = "";
for (int page = 1; page <= pdfReader.NumberOfPages; page++)
{
ITextExtractionStrategy its = new iTextSharp.text.pdf.parser.SimpleTextExtractionStrategy();
PdfReader reader = new PdfReader((string)pdfTemplate);
extracttext = PdfTextExtractor.GetTextFromPage(reader, page, its);
extracttext = Encoding.Unicode.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.Unicode, Encoding.Default.GetBytes(extracttext)));
pdfText = pdfText + extracttext;
pdfText = pdfText.Replace("[xyz]", s);
pdfReader.Close();
}
CreatePDF(pdfText);
}
catch (Exception ex)
{
}
finally
{
}
}

Answer 1

You are making one wrong assumption after the other.
You assume that the concept of "lines" exists in PDF. This is wrong. In Text State, different snippets of text are drawn on the page at absolute positions. For every "show text" operator, iText will return a TextRenderInfo object with the portion of text that was drawn and its coordinates. One line can consist of multiple text snippets. A text snippet may contain whitespace or may even be empty.
You assume that all text in a PDF keeps its natural reading order. This should be true for PDF/UA (UA stands for Universal Accessibility), but it's certainly not true for most PDFs you can find in the wild. That's why iText provides location-based text extraction (see p521 of iText in Action, Second Edition). As explained on p516, the text "Hello World" can be stored in the PDF as "ld", "Wor", "llo", "He". The LocationTextExtractionStrategy will order all the text snippets, reconstructing words if necessary. For instance: it will concatenate "He" and "llo" to "Hello", because there's not sufficient space between the "He" snippet and the "llo" snippet. However, for reasons unknown (probably ignorance), you're using the SimpleTextExtractionStrategy which doesn't order the text based on its location.
You are completely ignoring all the Graphics State operators, as well as the Text State operators that define the font, etc...
You assume that PDF is a Word processing format. This is wrong on many levels, as is your code. Please read the intro of chapter 6 of my book.
All these wrong assumptions almost make me want to vote down your question. At the risk of being voted down myself for this answer, I must tell you that you shouldn't try to "do the same". You're asking something that is very complex, and in many cases even impossible!