Library of Congress explains the difference
Although the terms are commonly lumped together, preservation and restoration are distinctly different efforts.
- Preservation can be thought of as any effort to keep a film in a viewable form, (and) most archivists consider a film preserved only when it is both (1) viewable in its original format with its full visual and aural values retained, and (2) protected for the future by preprint material through which subsequent viewing copies can be created.
- Restoration, by contrast, is defined as the reconstruction of the most authentic version of a film, (which) requires comparison of all surviving material on a given title, consultation of printed records of the production and exhibition history, and then decisions regarding the film’s “original” state.
— “Redefining Film Preservation: A National Plan,” Library of Congress, 1994