There are multiple ways to do this. I am using PyCharm 2019.1, but I bet that it will work in previous versions.
Find in path shortcut:
⇧ + ⌘ + F (mac) or
Ctrl + ⇧ + F (windows or linux)
This will open the following in which you can type the word you are looking for.
Find action shortcut
⇧ + ⌘ + A (mac) or
Ctrl + ⇧ + A (windows or linux)
The following will be opened in which you could type Find, and select the option Find in Path (notice that the command for this action is displayed next to it). After selecting this, you will be taken to the same menu that is opened when running the Find in path shortcut.
Right click on your project's directory, and choosing Find in Path...
You can right-click on your project's name, and select the option Find in Path... which will also open the menu that is opened after running the Find in Path shortcut.