You may be able to download the original installer from your Adobe account (under "Plans & Products" or "Order History"). Otherwise, Adobe no longer provides CS4 installers, so you’d need to use an old installation disc.
Let’s break the keyword down:
Given that Adobe is now on its version (part of Creative Cloud), seeking out CS4 seems counterintuitive. However, the demand persists for several reasons: Adobe Indesign Cs4 Portable Mega