How do I copy paste when it is disabled? Is there any way?

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C#

copy-paste

I have a long text and want to copy-paste it in textboxes of a software. The software, unfortunately, has disabled this functionality. Is there any way to enter the text without re-typing it? Is there any software doing this? Could you please guide me to write a c# program doing this automatically? (i.e., gets the text and types it in that software.)

Any help will be appreciated.

Adding more details. The OS is windows 10. The environment of the software is like an autorun containing some textboxes which i installed it from a CD. I have to enter some long text in it while the copy-pasting is disabled and i have to type that long text again. So i am looking for a method to enter the text without retyping it

What I have tried:

Testing different softwares and shift+insert and ...