In my case, using a pre-existing virtualenv did not work in the editor - all modules were marked as unresolved reference (running naturally works, as this is outside of the editor's config, just running an external process (not so easy for debugging)).
Turns out PyCharm did not add the site-packages directory... the fix is to manually add it.

On Pycharm professional 2022.3

Open File -> Settings -> Python Interpreter, open the drop-down and pick "Show All..." (to edit the config) (1), right click your interpreter (2), click "Show Interpreter Paths" (3).

In that screen, manually add the "site-packages" directory of the virtual environment [looks like .../venv/lib/python3.8/site-packages (4) (I've added the "Lib" also, for a good measure); once done and saved, they will turn up in the interpreter paths.

The other thing that won't hurt to do is select "Associate this virtual environment with the current project", in the interpreter's edit box.

Make sure you project in Pycharm is configured to use the same python interpreter you have installed in your PATH

Different solutions to this problem:

First: you are not on the pycharm terminal but on the power-shell terminal (if so, use the drop-down menu to the right of the +)
edit: if you opened the file/folder without creating a project, pip won't work in it (using a virtual env anyway)

Edit 2 : I just came across a new case. On certain versions of PyCharm, there is only the Windows terminal, so you have to activate your virtual environment manually.

To do this, type .\<project path>\venv\Scripts\activate

You will have (venv) and everything will work again.

Second : you have a python3 environment (use pip3 instead)

Last : your path is badly configured (not a big problem, passing by python -m pip ... it will work (or python3 or other version installed))

Finally, except in very specific cases file->setting->python Interpreter allows you to install anything you want without command line

Hoping to have helped you ;}

The thing is that pycharm creates all of your projects inside a virtual environment. So the packages that you installed outside the virtual environment(global site packages) does not get inherited in to your project. There is a simple solution for that. When you create a pycharm project, make sure to check the "inherit global-site packages" checkbox as shown here.Then you'll be able to import all the packages to your virtual environment, provided they have been installed in your computer.

Alternatively you can install all the packages separately using "pip install" in the pycharm terminal. If the package has been installed outside the virtual environment, pip will use cached files instead of downloading the package again.

Or you can install the packages using Settings -> Project -> Project Interpreter as the other answers suggests.

It is a bug in Pycharm:
https://youtrack.jetbrains.com/issue/PY-57566/Support-PEP-660-editable-installs

Pycharm cannot (yet) deal with the advanced ways setuptools installs editable packages. Using either one of the following in your to be installed package should help:

• use a different build backend in pyproject.toml, for example hatchling.

• use compat flag at install time (pip install -e /Users/whoever/dev/my-package --config-settings editable_mode=compat) - this does not work in requirements files, though.

Should solve this problem. DISCLAIMER, I've only tested the hatchling version, works fine for me.

Background/WHY?

In site-packages, the file mypackage-0.6.77.dist-info/direct_url.json contains infos where the editable package can be found. Installed with hatchling, this file just contains a path. With setuptools (both with legacy setup.py or pyproject.toml), it contains a pointer to .pth file, and this is not understood by Pycharm.