1. It is strongly recommended to disable your antivirus. Click the Start menu, type Windows Security, and then click on it.

2. Click Manage settings.

3. Turn off Real-Time Protection and other protection features by clicking the respective button.

4. This is how it will look like after all the protection features are disabled.

5. Right-click on the ISO file and select Extract to.

6. Open the extracted folder.

7. Double-click on Setup.exe, and then click Yes if UAC pops up.

8. Click the Accept button.

9. Click Next.

10. Click Next.

11. Press the Install button, and then wait until the installation is completed.

12. Press the Finish button.

13. Open the subfolder as shown in the image below.

14. Copy Illustrator.exe.

15. Paste the copied file into this folder: C:\Program Files (x86)\Adobe\Adobe Illustrator CS3\Support Files\Contents\Windows.

16. Click Replace the file in the destination.

17. Press Continue.

18. You can now use the full version of Adobe Illustrator CS3.