There is a niche, semi-legal practice among collectors: Many comic shops and online forums trade "reader copies"—low-resolution scans of out-of-print comics that DC no longer sells or monetizes.
These are legitimate opportunities. They are usually watermarked but completely legal.
For example:
DC Universe Infinite does not allow PDF downloads. You must read via their app (iOS/Android/Web). However, you can screenshot panels or use offline mode for flight reading. This is the single best legal alternative to "DC Comics free download PDF."
To get your hands on legally and for free, you don't need to risk sketchy PDF downloads. DC offers several official ways to read their iconic stories without spending a dime. ⚡ Best Ways to Read DC Comics for Free DC Universe Infinite (Free Section): The official DC Universe Infinite