A file opens in read-only mode to prevent unintended changes or deletions. This access restriction ensures the file's contents remain intact and unmodified. Common triggers include the file being locked by another user/program, explicit file attribute settings, insufficient user permissions, opening from a write-protected location (like a CD-ROM), or accessing files directly from online sources/archives where the source shouldn't be altered. Essentially, it differs from standard editable mode by blocking any save attempts back to the original file location.

This is frequently encountered in collaborative environments. For example, multiple users might have access to a shared document stored on a network drive; opening it read-only allows them to view the latest content while preventing conflicting edits until they explicitly check it out. Similarly, critical database files or configuration settings are often opened read-only by reporting tools or scripts to ensure operational stability and data integrity.

The primary advantage is robust data protection against accidental corruption or loss. Key limitations are the inability to directly save changes and potential workflow interruptions. Users needing to edit must typically create a local copy or resolve the underlying cause (e.g., gain permissions, close an application holding the file lock). This enforced safety measure significantly aids data security in professional contexts.