Adobe does not officially distribute portable versions. Below is a community-sourced method for educational purposes. You should own a legitimate license for Adobe Photoshop CS3 (discontinued, but second-hand licenses exist).
Sometimes, you don’t need the neural filters. Sometimes, you don’t need 3D rendering or cloud syncing. Sometimes, you just need to crop an image, remove a background, or design a quick flyer without waiting ten minutes for a "background process" to finish. Adobe Photoshop Cs3 Portable Google Drive