PyCharm does not use the same python interpreter as the one you installed package for.
As @crissal said, you can use PyCharm package manager to install packages, or configure it to recognize the one you already have:
- In your cmd, type which pythonand you'll get something like/usr/bin/python(on win it might be different but doesn't matter). That's the path of your default interpeter.
- In PyCharm: Preferences->Project->Python Interpreter
- Choose path if listed, or Show all->+-> find and select path
- Now in top right corner of the window, next to run button, select interpeter dropdown and Edit configuration
- Select correct Python interpreter, give it a few moments PyCharm will figure out yournltkdependency
I would strongly suggest using virtual environment for each project, in order not to mix dependencies.