Gimp was born in Linux environment that includes a Ghostscript to edit pdf's.
Unlikely, in Windows you don't find such script already installed. You have to follow these easy steps before installing Gimp:

Download the last releases of GTK+ libraries and Gimp from www.gimp.org (the single file for Windows includes also the GTK+ libraries)

Go to sourceforge.net/projects/ghostscript
Look for package Ghostscript x.y
Download a prepared Windows distribution (e.g. gs861w32.exe)
Start the executable and follow the instructions of the installation procedure
Copy the executable gswin32c.exe (not the gswin32.exe) from the directory c:/program files/gs/gs8.60/bin of the ghostscript installation to the Windows directory (e.g. c:\windows or c:\winnt).
Install GIMP.

If you get an error importing a pdf file, probably GIMP still doesn't know where the Ghostscript libraries are located.
You can set an Environmental Variable into Windows following these steps:

Open the Control Panel
Double click on System icon
Go to Advanced System Properties
Click on Environment Variables
Click on New button of System Variables
Set Variable name: GS_PROG
Set Variable value: C:\Program Files\gs\gs8.61\bin\gswin32.exe (check the version: 8.61, 8.62, etc.)
Click on OK
Click on OK
Click on OK
Restart GIMP