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C# PDFSharp: Examples of how to strip text from PDF?

I have a fairly simple task: I need to read a PDF file and write out its image contents while ignoring its text contents. So essentially I need to do the complement of "save as text".
Ideally, I would prefer to avoid any sort of re-compression of the image contents but if it's not possible, it's ok too.
Are the examples of how to do it?
Thanks!

Extracting text from a PDF file with PDFsharp is not a simple task.
It was discussed recently in this thread:
https://stackoverflow.com/a/9161732/162529

Extracting text from a PDF with PdfSharp can actually be very easy, depending on the document type and what you intend to do with it. If the text is in the document as text, and not an image, and you don't care about the position or format, then it's quite simple. This code gets all of the text of the first page in the PDFs I'm working with:
var doc = PdfReader.Open(docPath);
string pageText = doc.Pages[0].Contents.Elements.GetDictionary(0).Stream.ToString();
doc.Pages.Count gives you the total number of pages, and you access each one through the doc.Pages array with the index. I don't recommend using foreach and Linq here, as the interfaces aren't implemented well. The index passed into GetDictionary is for which PDF document element - this may vary based on how the documents are produced. If you don't get the text you're looking for, try looping through all of the elements.
The text that this produces will be full of various PDF formatting codes. If all you need to do is extract strings, though, you can find the ones you want using Regex or any other appropriate string searching code. If you need to do anything with the formatting or positioning, then good luck - from what I can tell, you'll need it.

Example of PDFSharp libraries extracting images from .pdf file:
link
library
EDIT:
Then if you want to extract text from image you have to use OCR libraries.
There are two good OCRs tessnet and MODI
Link to thread on stack
But I fully can recommend MODI which I am using now. Some sample # codeproject.
EDIT 2 :
If you don't want to read text from extracted images, you should write new PDF document and put all of them into it. For writing PDFs I use MigraDoc. It is not difficult to use that library.

Converting pdf to text

I need to create a C# or C++ (MFC) application that converts pdf files to txt. I need not only to convert, but remove headers, footers, some garbage characters on the left margin etc. Thus the application shold allow the user to set page margins to cut off what is not needed. I actually have already created such an application using xpdf, but it gives me some problems when I am trying to insert custom tags into the extracted text to preserve italics and bold. Maybe somebody could suggest something useful?
Thanks.

There are shareware and freeware utilities out there. Try fetching their source code, or perhaps use them the way they are.
A public version of the PDF specification can be found here: Adobe PDF Specification
PDF Shareware readers can be found: PDF Reader source code # SourceForge

Please look at Podofo. It's a LGPL-licensed library that has many powerful editing features. One of it's examples, txt2pdf IIRC, is a good start: it shows basic text-extraction; From there you can check if pre (in pdf engine) or post (in text) filtering suffices to your goals. I didn't get to use Pdf Hummus, but it's supposed to have these capabilities too, although it's less straightforward.

Extract data from nested tables in PDF

I have a few pdf files that were created from word or excel files.
I need to get the information thats in the tables.
The text in the document is not an image so I'm able to extract the text using tools such as pdfbox.
When I have the text I have no way of knowing what cells in the table it belongs to because I don't know where the table borders are.
Iv'e tried a few desktop tools such as abby or solid pdf converter and they are able to convert the files into nice word documents but this doesn't suit my needs as I want to be able to do this programatticly in C#.
Some of the tables have nested tables wich I think makes this a little bit more diffucult.
I appreciate your help

The difficulty here is caused by the fact that the text in the PDF is not contained within any table. It might look like it is, but underneath the surface, it is not.
So there are a couple of options that I can think of. But none of them are going to be quite as satisfying as you'd probably like.
There are some companies that offer SDKs for PDF to Excel/Word conversion. Investintech and Iceni are a couple of examples. But these solutions are not free.
If you know the exact layout of the PDF files that you need to extract the table data from, then you can use any SDK that lets you extract text from a PDF and also tells you the exact co-ordinates of the extracted text. Using this method you need to know in advance where the text is going to be, so that you can extract text from a specific area on the page. It obviously won't work if you need to process any random document.
It's a difficult task, but hopefully this will give you a starting point.

Reading PDF file to get tabular data in structured format,

I have to read a pdf file which contains a table with several columns. Using iTextSharp I am able to read the file but I get bunch of non-formatted text. I am not able to structure the data so that I can insert into a database.
Any suggestions?

Unless its structured text there is no tagging to show columns. Tools like PdfBox make 'guesses' to try and extract the table.
There is an article explaining why text extraction is so hard at http://pdf.jpedal.org/java-pdf-blog/bid/12670/PDF-text

If I understand it correctly, pdf text is stored positionally, so it has no concept of rows or columns. That means you have to use heuristics based on the "likelihood" that a you're reading from a different column.
You can try doing this by comparing the amount of space between the words. (I'm not familiar with the ITextSharp interface so please forgive me if I'm mentioning things its not capable of. . . I'm mostly familiar with pdfNet.
Another idea that just came to me is that if the text has visual cues such as vertical lines separating the columns. If that's the case you should be able to come up with heuristics to determine if the text is left or right of the column lines.
...
However the best thing to do, if possible, is to get ahold of the data in a more database friendly format. This will likely save heartaches in the long run.
-- Jason

I am concluding there is no straight forward way to do this. Atleast reading the data in tabular format. I tried suggestions provided by Mark, but it is seems to be not feasible as per my requirement.

Is there a way to replace a text in a PDF file with itextsharp?

I'm using itextsharp to generate the PDFs, but I need to change some text dynamically.
I know that it's possible to change if there's any AcroField, but my PDF doen's have any of it. It just has some pure texts and I need to change some of them.
Does anyone know how to do it?

Actually, I have a blog post on how to do it! But like IanGilham said, it depends on whether you have control over the original PDF. The basic idea is you setup a form on the page and replace the form fields with the text you want. (You can style the form so it doesn't look like a form)
If you don't have control over the PDF, let me know how to do it!
Here is a link to the full post:
Using a template to programmatically create PDFs with C# and iTextSharp

I haven't used itextsharp, but I have been using PDFNet SDK to explore the content of a large pile of PDFs for localisation over the last few weeks.
I would say that what you require is absolutely achievable, but how difficult it is will depend entirely on how much control you have over the quality of the files. In my case, the files can be constructed from any combination of images, text in any random order, tables, forms, paths, single pixel graphics and scanned pages, some of which are composed from hundreds of smaller images. Let's just say we're having fun with it.
In the PDFTron way of doing things, you would have to implement a viewer (sample available), and add some code over a text selection. Given the complexities of the format, it may be necessary to implement a simple editor in a secondary dialog with the ability to expand the selection to the next line (or whatever other fundamental object is used to make up text). The string could then be edited and applied by copying the entire page of the document into a new page, replacing the selected elements with your new string. You would probably have to do some mathematics to get this to work well though, as just about everything in PDF is located on the page by means of an affine transform.
Good luck. I'm sure there are people on here with some experience of itextsharp and PDF in general.

This question comes up from time to time on the mailing list. The same answer is given time and time again - NO. See this thread for the official answer from the person who created iText.
This question should be a FAQ on the itextsharp tag wiki.