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Determine who has a file open using C# - is there a way now?

I need to be able to check who has a file open using C#. I found a few people asked this question before but they were all a long time ago with the latest being in 2012. I was wondering if, in the last 5 years, has Microsoft added this ability to .net or maybe someone came out with a nuget package that is capable.
Here is the latest answer I found

You can use windows internal function NTQuerySystemInformation with undocumented parameter SystemHandleInformation for it. I don't know about c# implementation, but I know delphy code for it, and vb6 code. Check this links, it will help you to make your c# implementation.
Delphi - get what files are opened by an application
https://forum.sysinternals.com/topic14546.html

As far as I know, the standard library still does not have suitable functions for this. There is a popular question about this: https://stackoverflow.com/a/937558/5665527.
Also, if you want to know who opened the file remotely - net file function may be useful (which is accessible via cmd). I believe that there are similar WinAPI functions on MSDN that could be implemented in a similar way.

C# led panel controlling over ethernet with native dll

Hy,
I had bought a "Huidu HD-E40" led panel a few days ago and the company sent me a .dll file. (I mean, it wasnt written in .Net). My question was the following: How can I use the file contents in C#. I had registered the dll via regsvr32, then added to the project reference but it seem like incompatible. I need some advice how to start with this projekt. I'd just like send a short string to the display via ethernet port. Sorry for my bad english, I'm a greenhorn from Hungary.
There are the file, that I've got for reference
http://wikisend.com/download/349890/Huidu_DLL_Reference1.doc

I know the question was asked more that 7 years ago, but for those who are looking for info on the SDK:
If you are referring to the HDSDK.dll which can be found in the Huidu_Gen6SDK_V1.9.zip then you need to use it with P/Invoke as that dll is not a .NET assembly but a native one. As #Kwang suggested if you would be able to download the SDK from their webpage there would be a complete C# demo.
Unfortunately it isn't available anymore, so you need to use the wayback machine to obtain it from here: https://web.archive.org/web//http://download.huidu.cn/download/

I think you need download the lastest version of HDSDK in the home page.It is contain some demo with C, C# and vb.net. Im using it for my project but it missed function create digit.

Integrating Microsoft Office Communicator 2007 R2 - Samples?

Basically, I can't seem to find any good resources out there for examples. I attempted to download a couple of msi from microsoft.com, and one of them included isntalling a solution file (.sln), but when I open the solution I can't actually compile the application.
Basically, what do I need to actually get started with getting the necessary libraries and sample code?

A good resource to get started is the Programming for Unified Communications book - this covers R2 quite well. Check out the answer here for a bit more detail

Working with DjVu with .NET

I need to open DjVu files in my program, so I'm looking for some library. It must be free library, opensource would be better. When I tried to google it, I found only links to some books about .Net in *djvu format :D

This is an old question, but I wanted to include that I just uploaded a fully managed Djvu reader written in C#. If you make improvements please share. https://github.com/Telavian/DjvuNet

The following techniques may be useful.
First technique:
1) http://javadjvu.foxtrottechnologies.com/ djvu support for java
2) use ikvm.net to convert java code in dot net
it is tedious but can be tried and i think best method
Second technique:
http://twit88.com/blog/2009/02/28/open-source-windows-djvu-viewer/
a viewer to open djvu files
for more detail go through
sourceforge djvu
you can get basic details from here

How to write FireFox extension with Visual Studio using C# programming language?

I was wondering if it's possible to write Firefox extension using .Net Framework?
Had anybody such experience in writing Firefox extensions using C# programming language?
Any good sites or guidelines would be very helpful.
FFPlugin http://img81.imageshack.us/img81/3049/ffplugin.jpg
Here is an example of what I need. Extension to enter phone number and to send SMS Message.
I draw it in Paint, so I'm sorry for having no artistic touch.

Assuming you're asking about writing an extension (and not a plugin), the best place to get started is with the info at the Mozilla Dev Center.
Konamiman is correct: extensions are mostly XUL (an XML grammar) and Javascript, packaged into a ZIP file with the extension .xpi. The various links from the page I linked should answer basic questions, like the one you posted above:
https://developer.mozilla.org/en/Building_an_Extension
https://developer.mozilla.org/en/Extension_Frequently_Asked_Questions

Firefox extensions are written primarily in Javascript. See here: http://www.rietta.com/firefox/Tutorial/backend.html. So unless you can find a way to convert C# code/.NET Framework objects to Javascript, you are out of luck.

As has been observed by other respondents, Firefox extensions are primarily written in Javascript: but you're in luck, because Script# is a free tool that enables developers to author C# source code and subsequently 'compile' it into Javascript.

I'm not sure how you'd do for C#, but you can use XPCOM to call native code libraries: that's how the Glasser extension, for instance, is able to use the Windows-specific Aero effects.
IBM hosts a very good XPCOM tutorial at DeveloperWorks.