如何使用itextsharp从pdf获取特定的列值

Question

I have a PDF in which data is displayed in a table. In this table, I have multiple columns, but I want to get particular column values as a list. Is this possible?

This is my code:

PdfReader pdfReader = new PdfReader(fileName);
for (int page = 1; page <= pdfReader.NumberOfPages; page++)
{
    ITextExtractionStrategy strategy = new LocationTextExtractionStrategy();
    string currentText = PdfTextExtractor.GetTextFromPage(pdfReader, page, strategy);
    currentText = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.UTF8, Encoding.Default.GetBytes(currentText)));
    text.Append(currentText);
}
pdfReader.Close();
return text.ToString();

With this code, I get all of the text of the PDF, but I want a particular column of data. The column name is "Date".

Answer 1

This is much more complicated than you would think. A PDF document does not (always) contain structure information. It only has instructions that a viewer needs to render the document.

Imagine something like:

go to 50, 50
use font Helvetica Bold
draw the glyph for character 'H'
go to 56, 50
draw the glyph for character 'e'

These instructions do not even need to appear in logical reading order. As a result, determining what makes up a logical table, based on instructions is very hard.

Possible approach (if your table contains enough lines):

• use IEventListener to be notified of PathRenderInfo and TextRenderInfo
• gather PathRenderInfo into lines
• gather lines into clusters if (and only if) they cross at 90° angles
• determine number of rows and columns from such line clusters
• assume something is a table if (and only if) it consists of enough rows and columns and has some text in it