The difference between typing and copying/pasting depends on the program that you’re using.
In an ideal world, the program would not know whether characters were typed in or pasted from the clipboard. Most programs really have no need to know or care about the difference. In fact, many applications are simply not involved in the process whatsoever.
Many, but not all.
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Windows common controls
Many applications use Windows standard or common controls. When you’re typing into a field in a program or on a web page, it’s actually a Windows common control that handles character entry – whether something is copied to or pasted from the clipboard, being typed in, or some kind of combination.
The program that’s receiving the data? It doesn’t know. In fact, it’s not even involved until everything is done and the person hits Enter, OK, or whatever.
Some applications need more control
On the other hand, some programs are deeply involved in the whole copy/paste process.
A good example would be a word processor. There are so many different types of content and different types of formatted information, that the application needs to make some decisions as to exactly how to treat that data when it’s pasted in. When that happens the application absolutely is involved in processing the paste, and potentially transforming the data or its formatting according to whatever its own internal needs might be.
Proving it after the fact
But can that involvement be detected or proven?
Theoretically, the answer is no. Theoretically the result of typing should be no different than the result of pasting that same text in. Once you have the data in your document or form, it’s just data with no real indication of its source.
I have to say “theoretically”, since there’s actually nothing that prevents a program that knows about copy/paste to somehow include the information in its file format, either explicitly for some reason, or as a side effect of a complex file format. In my opinion the chances of this are exceptionally slim.