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.NET graphic libraries to display images (pdf, .docx and any other format of image) in the browser

I am developing a ASP .NET MVC application where users are able to upload files to a repository. Those files could be pdf, doc, any type of image and so on.
When the user select a file to be imported I would like to display this file in the browser so they can review its contents before the upload.
I know I could use some sort of IFrame to display pdf but I am looking for some specific class or .net libraries to implement this feature.
I just need a north.

This is an extremely difficult problem. There are some libraries that can help. For instance PDF files might be rendered to images with ghostscript. Word and Excel files might be converted to PDF or image with a number of libraries. None of them, AFAIK, are very good at it so I can not recommend one.
You could automate MSO to perform the conversion to PDF, but that is decidedly not safe for server code. Another possibility is convert source documents to SWF files (like flexpaper) and display in flash. There are some great libraries out there, but it will limit your supported clients. Sharepoint has support for providing some of this capability as well. Others have used OpenOffice to convert MSO documents but also at a loss of quality.
I can't really advise any specific direction as it is highly dependent on what you/your company is willing to spend and the desired results. Good luck.

You could try to rely on Windows and the explorer thumbnails for it, like here, but then you'd have to make sure that:
You can abuse the server in the most elaborate way (install stuff, talk to the shell from ASP.NET)
You have a thumbnail provider installed on the server for every type that you want to preview. I guess from the moment you can see the thumbnail in explorer, you're set. So for pdf, you might need to install PDF Reader from Adobe.
Docx files should be saved with thumbnail checked (see link). There seems to be no other easy, free way to convert a docx to a thumbnail. The "best" solution I came across, was saving it automatically again somehow, and making sure the thumbnail option is checked.

I don't want to say that's impossible, but it can't be done with finite effort.
What you are asking for is a browser-based solution, because you want the user to be able to "review" the document before uploading.
Therefore you cannot use a server side solution, which is essentially what is being asked by referring to a ".Net library".
.Net libraries are dependent on an installed version of .Net, which does not exist in all versions for all operating systems for which graphical browsers exist.
Next, recent changes in browser security do not allow to read the full client-side file name of the selected file in the input field.
You'd have to rely on HTML5 and its FileReader to access the file's byte stream, but even then you can only retrieve image from image files. (see sample)
Excluding browser-based solutions in Flash, ActiveX, Java, due to browser and platform support, this leaves JavaScript as the only "reasonable" solution: you'd need a library for each supported format to either convert a file into an image in an image format supported by browsers, or extract the text(+image) representation of a file.

Great awnsers... Just want to share the result of my research and I found a nice client-based solution supported by Mozilla Labs. This is a framework based on HTML5 and Javascript with no native code needed.
Here the project website:
https://github.com/mozilla/pdf.js
This is what you are capable of:
http://mozilla.github.com/pdf.js/web/viewer.html
And for the last a great video explaning how everthing works
http://www.youtube.com/watch?v=Iv15UY-4Fg8&noredirect=1
Reguarding my question we are going to converter every possible file to PDF on the server and then render this PDF using this framework.

How to connect to a print driver in C#?

I have an task of converting bunch of formats like .pdf, .doc, .jpg, .xls, .txt, .bmp file types into .png format. I found a print driver that does that.
But how do I connect to that printer driver in .net? This will a server side component. I need to print documents into a folder using this print driver.
I am wondering how that can be done.
Thanks

Based on your updated comments, it sounds as if you are looking to convert a variety of images and document types to a single common image type. The process of taking one of the several possible source formats you mention and convert it to a bitmapped format such as .PNG is referred to as RENDERING or RASTERIZING. You want to take one of the input formats, render it to a bitmap representation, then write it to a file in .PNG format. While it certainly might be possible to do this using a print driver, to do so, you would typically be relying on an installed application that would allow you to pass the source document to it for printing to the driver. For this to work, each of the source file types you want to be able to handle this way needs to have an application installed which can take actions from the shell and do what you request. So for example if you want to do this with a .DOC file, you need Microsoft Word installed as it does properly respond to the PRINT shell command. However, the limitation with the shell based method is that it is always going to print to the DEFAULT system printer. So your driver would need to be setup as the default printer for the machine you are going to run your process on. Therefore you would need to see if each of the source types you want to be able to handle have an installed or installable application which will allow you to print them using the shell and the PRINT action verb.
Reference URLs:
Windows Shell Verbs and File Associations
Creating Shortcut Menu Handlers
The problem with this technique is not all applications respond to the PRINT verb correctly or at all. This usually works with all the major Microsoft applications, but you should test any other document types you want to support before going much further with this technique.
This also raises other questions that this doesn't even begin to address such as what to do about multiple page formats. You listed a few image types that are straight-forward and can be converted to PNG files pretty directly. But how do you want to render a multiple page Word document files into PNG format? Do you intend for only one very large PNG with all the pages one after another? Or do you intend for one PNG file per corresponding source document page? The print driver method might not give you very much control over that.
Depending on some of these details and just how much control and reliability you need in the process, you might want to consider a completely different route to your process. Maybe you should consider using tools/libraries that can read the source file formats you want to support and render them directly, after which you can save into your PNG files. One library I have used in the past that would seem to fit and allow you a high degree of control over the conversion (rendering/rasterization) process is LeadTools. It is a fairly pricey product, but my experience with it has been that it does support a wide variety of formats reliably.
LeadTools PDF and Document Readers SDK
There may be some other open source tools available that you could pull together to support this type of functionality, but I'm not familiar with any to point you to anything specific. But hopefully this helps give you some information to look at putting together a process that might be more reliable and give you greater control than trying to coerce a printer driver to do something you might not quite be able to make work reliably.

Server-side component implies something that doesn't have a human sitting at it (at least, not the human that is trying to use that printer). If this is the case then a print driver will not work - Print drivers that write their output to disk instead of a device always, in my experience, ask the user to select a place to save the file (present a Save As dialog).

To elaborate a little bit on what Boo mentioned :
Depending on the printer driver you are using, you may be able to tell it where to save your file.
The problem is by using a printer, how it normally works is that you can print from any application to a .png file. But the application itself has to know how to open and render (not talk to the printer) the content of the original file.
To continue down this path, you have to make sure your server component knows how to read and render content of each file type (.jpg, .pdf, .doc, etc.).
Assuming your server component knows how to render the content, the next step from here is to use the .NET Printing namespace to print your content to the .png printer.
For more details go to : http://msdn.microsoft.com/en-us/magazine/cc188767.aspx

Open docx in Windows Phone 7 programmatically

I would like to develop an app for printing service in Windows Phone 7. In the app, the users can select file to print out. Is there any way to open docx, xlsx, etc. in WP7 programmatically? I know in iPhone the WebView supports to view many file types. Is there anything similar in WP7?

If you are looking to open the document in Office, try using the WebBrowserTask to navigate to the document. There's a good chance it will open with Office.
If you want to render the document yourself, you are very much out of luck. You could try navigating to the document in a WebBrowser control, but I don't think it's supported.
Besides, there are no printing APIs so there would be no way to print it. If this is an enterprise application (ie. internal to your company), you might consider writing a web service on a local server that can accept DOCX files and print them. You could then call that service from your app to print the docs.

You will not be able to open these types of files from the isolated storage. There is no way for third-party applications to launch the external application required for viewing these file types. All of the files which you have listed in your question are XML-based open source file formats. Depending on how much time you want to spend on this, you could write your own parser or possibly utilize an open-source or commercial one.

Reading an STG file created from MS ActiveSync

How can I parse an STG (Microsoft ActiveSync Mobile Device Backup) file (created by ActiveSync)?
I have an old .stg file that was created from backing up an old Windows Mobile device, and I would like to write a program to read it using C#. I have tried a few things but can't get anything but garbage when I read through it. From what I can find online it is stored in Unicode format but that's about it, any posts I find talking about it are ancient and all the links are dead.

You can open ActiveSync .stg files in an archiver tool such as 7-Zip or PeaZip. If the program does not recognize the file as an archive, you may need to rename the file to have an archive extension (e.g., .7z, .gz, .tar).

With PeaZip is also possible to try to open any file extension from "Open as archive" menu entry (also available in system's context menu), without changing the file's extension.
With many format being basically variations of Deflate-compressed containers, it is worth trying.
Anyway, some formats may introduce proprietary fields (e.g. extra checksums, comments, digital signing, etc) which are out of the scope for a general-purpose archiver as PeaZip or 7-Zip.
So, while it is harmless to try to read container files as archives, it is not adviceable to try to edit them as such.

how to create a custom file extension in C#?

I need help in how to create a custom file extension in my C# app. I created a basic notes management app. Right now I'm saving my notes as .rtf (note1.rtf). I want to be able to create a file extension that only my app understands (like, note.not, maybe)

As a deployment point, you should note that ClickOnce supports file extensions (as long as it isn't in "online only" mode). This makes it a breeze to configure the system to recognise new file extensions.
You can find this in project properties -> Publish -> Options -> File Associations in VS2008. If you don't have VS2008 you can also do it manually, but it isn't fun.

File extensions are an arbitrary choice for your formats, and it's only really dependent on your application registering a certain file extension as a file of a certain type in Windows, upon installation.
Coming up with your own file format usually means you save that format using a format that only your application can parse. It can either be in plain text or binary, and it can even use XML or whatever format, the point is your app should be able to parse it easily.

There are two possible interpretations of your question:
What should be the file format of my documents?
You are saving currently your notes in the RTF format. No matter what file name extension you choose to save them as, any application that understands the RTF format will be able to open your notes, as long as the user knows that it's in RTF and points that app to that file.
If you want to save your documents in a custom file format, so that other applications cannot read them. you need to come up with code that takes the RTF stream produced by the Rich Edit control (I assume that's what you use as editor in your app) and serializes it in a binary stream using your own format.
I personally would not consider this worth the effort...
What is the file name extension of my documents
You are currently saving your documents in RTF format with .rtf file name extension. Other applications are associated with that file extension, so double-clicking on such file in Windows Explorer opens that application instead of your.
If you want to be able to double click your file in Windows Explorer and open your app, you need to change the file name extension you are using AND create the proper association for that extension.
The file extension associations are defined by entries in the registry. You can create these per-machine (in HKLM\Software\Classes) or per-user (in HKCU\Software\Classes), though per-machine is the most common case. For more details about the actual registry entries and links to MSDN documentation and samples, check my answer to this SO question on Vista document icon associations.

I think it's a matter of create the right registry values,
or check this codeproject's article

You can save file with whatever extension you want, just put it in file name when saving file.
I sense that your problem is "How I can save file in something other than RTF?". You'll have to invent your own format, but you actually do not want that. You still can save RTF into file named mynote.not.
I would advise you to keep using format which is readable from other programs. Your users will be thankful once they want to do something with their notes which is not supported by your program.