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Take a screenshot behind window in C# WinForm

I'm working on an app in c# windows forms, I have a form called Form1 with a button, and after click this button the idea is to take a screenshoot of everything behind it except the Form1 itself (without minimizing Form1).
Any idea or suggestion?
Thank you!

If you want a solution without hiding, moving, minimizing etc., you need the following approach:
EnumWindows() to iterate all windows. This will give you the windows top to bottom.
Don't forget to exclude your own window
Exclude windows that are invisible. Check out GetWindowLongPtr with GWL_STYLE and compare against WS_VISIBLE
GetWindowRect() to get their size
PrintWindow() to get a bitmap of the window, no matter whether it's in the background
Create a bitmap with the size of the VirtualScreen
Paint the windows in reverse order (bottom to top) using DrawImage()
I found that this is quite fast (514 ms on a 2560x1440 screen with 20 visible windows to draw).
Limitations:
since it sends a WM_PRINT message to the application, you can not capture applications that are "not responding"
For me, Firefox does not render well. It's missing page contents.
For me, control panel content appears black, although it's there when getting a screenshot of the whole screen.

you can use hard code. Actually light shot and other tools working such as. When you click to screenshot button you may close the form window after the event and reopen it. it is the basic way of solution...
Please check this way: How can i capture the screen without the Form?

Getting Pixel Values "Under" Current Window

I'm trying to make, essentially, a screen capture program, that captures the pixel values under the current window. (I'm working in C#, in Visual Studio 2015.) However, for various reasons, the window itself needs to be opaque (for filters and such). How can I best achieve this?

It is possible to find the window below yours and get a screenshot of it even if it is hidden with the method: PrintWindow (see PInvoke.net as well)
See Copying content from a hidden or clipped window in XP?

It is very simple to do in Winforms. Just set the form's Opacity value to 99%. Now Graphics.CopyFromScreen() will not see your window anymore.
Except when the window underneath yours is also a layered window, then it also won't be visible to CopyFromScreen() for the same reason. Then you have to set Opacity to 0, copy and set it back to 0.99. Very quick, probably good enough for what you want to do.

Custom Shaped Aero Windows in C#? Like THESE!

How do I make an irregular shaped Aero window like this one?
Look in the lower right corner!
This program also does it.
This also does it! >_< Even more...

I recently used this solution and it worked for me:
http://devintelligence.com/2007/10/shaped-windows-in-wpf/
I had to create a separate assembly containing the WPF form because the rest of my project uses WinForms. From there it's quite straight forward: Use a background image with transparency and set the form to transparent.
Though you might need to change WindowStyle="None" to something other or else
you'll have no close button etc.

Vista Style DropDownMenu with TrackBar

In Windows Vista/7's windows explorer, the Icon Size selector has got a track bar in the DropDownMenu (see Fig. 1)
Fig. 1: DropDownMenu with TrackBar in Windows Vista
Does anyone know where I can get a similar UserControl or show me how to replicate it in .NET?
NOTE: If anyone's wondering where the image came from, I captured it from Windows Vista's Windows Explorer when I clicked on the Views Button.
Edit
I realised that Trilian 5 beta also has something similar. I'll try to get a screenshot of it soon enough.

I have found an article at CodeProject. It allows such a menu. This will be of assistance to you.
WPF Slider Menu
http://www.codeproject.com/KB/WPF/WPF_Slider_Menu.aspx

Windows Forms advanced visual effects

I have an design idea about the appearence of a small program , which is basically a windows form with a combo and one button.What i would like to do is the following.When i click on the .exe of the program to start it , i would like to have an non-standart start up of the window.To be more specific i will give you an example - i click on the .exe , upon which some dots appear in a random matter all over the screen , after those points appear they start moving in a spiral way so finally they merge into the standart square windows form shape.So my question is - is there a free API or anything similar with the help of which its easily doable or there would be a lot of work needed from myself to create those API's ?
Thanks in advance

This will be extremely difficult to do.
It will also be very annoying for the end-users.

In short I see two options:
Render your form to a bitmap and render peices of the bitmap to a full-screen layered window. You'll have to call UpdateLayeredWindow repeatedly to get the animation working but that should be a good lead. I could see getting 10-20 fps with this method.
Take a screenshot of the desktop, create a full screen borderless topmost window, render the screenshot, then render your animation on top. This will prevent any other windows from recieving input while the animation is playing.
Either way your users will hate you.

As SLaks has already said, that will be pretty annoying for the end-users.
If you ask whether it is doable, I would say yes, everything is doable in programming, it all depends on the effort you're ready to put into.
As a very simple algorithm, here are some steps I would go through for your achievement:
Create a System.Windows.Forms.Form;
Set Form.ShowInTaskBar= false;
Set the Form.TransparencyKey property;
Set the Form.ControlBox= false;
Set Form.TopMost= true;
Drop a PictureBox control on your Form;
On the Form.Load event, take a screenshot of the current desktop and set it as the image of your PictureBox.
Then, build an animated GIF, and superpose it to your form.
You will most likely appreciate, I guess, the following link which discusses about C# Winforms Animation.
Disclaimer: This is an arbitrary algorithm off the top of my head. Besides, I illustrated the steps I would go through in order to achieve such objective, though I have never ever performed WindowsForms animation.
Althouth this might be cool to program, users are conservatives and "always anxious" about program startups, so, as already mentioned, this might become pretty annoying for the end-users.
I hope this helps you through anyway!