Send document to printer with C#

The key phrase in that question is 'web application'.

In a normal web app using only HTML+Javascript over HTTP, you can't just send a document directly to a printer. That's one of the reasons web browsers exist, and without that functionality everyone's printer would collect the same kind of junk that a public fax machine does.

So you need some kind of work-around. One option is to build on a common plug-in, like flash, silverlight, java applet, or even something like greasemonkey. Another is a custom plug-in, like a hosted winforms control or custom browser extension.

You are very fortunate, in that it looks like you have complete control (or knowlege of) the deployment environment, and that this environment if fairly homogenous. This means you have an additional option that others have started to explore. If you can install all of the printers in your environment to the web server, then it's fairly easy using the built-in .Net printer classes (in the System.Drawing.Printing namespace) to list out those printer, either show them to the user so they can pick or keep some kind of IP to Printer mapping table, and then print directly to that printer from your web app. Note that this scheme may require your app to run at a higher level of trust than would otherwise be required.

Now it comes to actually printing your PDF's and word documents. For acrobat, check this link:
http://support.adobe.com/devsup/devsup.nsf/docs/52080.htm (Wayback machine)
Note that it's a little dated, but I believe the concept is still valid. You'll have to experiment some to make sure it works as expected.

For Word, I'm not normally a fan of Office interop/automation in a web app. But in this case you're not editing any documents: just loading it up long enough to print. And the fact that you're relying on another scarce resource (the printers) should keep this from scaling beyond what your web server could cope with. So you may have a rare case where Office automation in a web project makes sense.

Many printers and multifunction devices today support the printing of PDFs directly, this may solve one of your problems. Simply have the PDF sent to the printer. In fact, some even support the sending of a URL and the printer will then go get the document and print it. Lexmark for sure does this and I think a few other vendors do as well. This still mean you have to deal with the Word document. Word 2007 supports PDF (with the add-in installed from Microsoft) and I've used this function programatically with great success in C#.

Here's the code for that:

Microsoft.Office.Interop.Word.ApplicationClass msWord = new Microsoft.Office.Interop.Word.ApplicationClass();

object paramUnknown = Type.Missing;
object missing = Type.Missing;
object paramSaveChangesNo = Microsoft.Office.Interop.Word.WdSaveOptions.wdDoNotSaveChanges;
//object paramFonts = Microsoft.Office.Interop.Word.wde
object paramFormatPDF = Microsoft.Office.Interop.Word.WdSaveFormat.wdFormatPDF;
object paramTrue = true;
object paramReadOnly = true;  
object sourceDoc = @"c:\input.doc"                              
object target = @"c:\output.pdf";

msWord.Visible = false;

//open .doc
msWord.Documents.Open(ref sourceDoc, ref paramUnknown, ref paramReadOnly, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown);

//so it won't show on the taskbar
msWord.Application.Visible = false;
msWord.WindowState = Microsoft.Office.Interop.Word.WdWindowState.wdWindowStateMinimize;

//save .doc to new target name and format
msWord.ActiveDocument.SaveAs(ref targetDoc, ref paramFormatPDF, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramTrue, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown, ref paramUnknown);

msWord.ActiveDocument.Close(ref missing, ref missing, ref missing);

msWord.Quit(ref paramSaveChangesNo, ref paramUnknown, ref paramUnknown);

Lastly, if your device doesn't support PDF printing then you could use Ghostscript or other tools to convert your PDF to PS or even PCL. Not the greatest as this mean running a little unmanaged code or worst case, shelling out and executing the GS command line, that being said, we currently do this in one of our web apps and it works well. As an aside, we don't do it for print but rather the joining of a number of PDFs togheter, but in the end it will work the same.