I paste a picture in the document and after I opened the file the picture became a black square how do I return it to be a picture?
Can you try View > Preview on CPU?
Have you tried placing the file instead of pasting it? File > Place is the recommended way to insert images into an Illustrator document.
It was a picture and turned into a black rectangle
If you select it what do you see in the Links panel?
(And what Monika and SJRiegel asked)
In the link window it also looks like a black rectangle
When I preview in the CPU nothing changes
What kind of picture is it?
What if you open it in Photoshop and resave it in an appropriate format?
I do not have it in Photoshop
I copied it from a clipboard
But why did it happen?
Illustrator cannot handle each and every file format with all the possible options. So how about opening it in Photoshop and then resave it?
The image file may not have been linked, so when you re-opened the file, Illustrator could not find the original. If you pasted from the clipboard, the image preview could also have become corrupt. Best practice is to save your images in a folder dedicated to a file. What I do is create a directory ( not sure that is the right word ) folder ( i.e., JOB060221A = main folder > inside that are two folders: 1.) Illustrator Files; 2.) Photoshop Files > save images in the Photoshop folder, save your document in the Illustrator Files folder using whatever name you want. As suggested already, you typically "Place" an image file inside your Illustrator document. When you "Place" the image, you can set it to become linked to the original file which exists in the Photoshop folder. This becomes a nested system where everything can be found in one folder. When you pasted from the clipboard, the original file really never existed, so Illustrator put a placemat ( i.e., black rectangle ) in its spot. Just have to find the original image and "Link" it to your document ( try not to embed image files, your file quickly becomes bloated ).
Also, when you paste from the clipboard that is a temporary file. As soon as you copy > paste another file, the other file is lost, no longer exists in the clipboard.