Some trial and error is required, slowly searching through frames. This makes microfilm a tedious media to use. Still another problem is that, when the original documents are filmed, there is no way to tell if they have all been captured successfully. It is only after the film has been processed that errors or omissions are found. Yet even with these problems, microfilm has until recently been about the only choice for long term storage.
Many companies have years and years of documents stored on microfilm.
In some cases, the original documents have long since be destroyed. Today, it is possible to convert microfilm, microfiche, and even aperture cards into digital images. A specialized microfilm scanner is used to do this. The roll film, or fiche, or cards are fed into the scanner, which works somewhat like a microfilm reader. It advances the film to the first image, projects a beam of light through it, and records the image digitally.