Calibre turns a collection of separate e-book files into a managed library. Adding a book creates a managed copy inside the chosen library folder, reads available metadata, and places the title in a searchable database. The file originally dragged into the library remains untouched. Work done there affects the managed copy and records, which is different from renaming or moving the original file in File Explorer.
Managed library
The library folder is the whole collection, not a loose destination for book files. Calibre arranges book copies under author and title folders and stores the collection index in metadata.db. The program controls that structure. Manually adding, renaming, or removing files inside it can leave the database and folder contents out of agreement, and later library operations may move or delete unmanaged material.
One book record can hold more than one format. EPUB and PDF copies of the same title can remain attached to one metadata entry rather than appearing as unrelated books. The record can also carry a cover, tags, comments, identifiers, and custom columns. Editing these fields changes the library record; it does not necessarily rewrite every piece of metadata embedded inside every book format until a separate write or conversion operation does so.
Format conversion
Calibre can convert a stored book into a format required by another reader or workflow. Conversion interprets the source document, applies settings for page layout, fonts, structure, and the table of contents, then writes another format into the same book record. It does not turn every source into a visually identical copy. A PDF built around fixed page coordinates behaves differently from a reflowable EPUB, and difficult layouts may need conversion settings or later editing.
The internal viewer opens supported formats, while configured formats can open in the operating system’s usual reader. A right-click on View selects a particular format when a record contains several. Create catalog performs another kind of output: it builds a catalog from the books and metadata in the current library rather than converting one selected title.
Device transfer
Connecting a supported reader adds device actions to the interface. Calibre can send a chosen format to main memory or a storage card, and it can apply a naming template to the destination folders. If the reader needs another format, conversion can occur before transfer. The copy on the device and the copy in the library then occupy separate storage; deleting one does not normally delete the other.
One menu choice deliberately breaks that expectation: Send and delete from library transfers the selected book and then removes it from the local library. It should not be treated as the ordinary Send command. Device detection can also fail when a cable, driver, storage mode, or unsupported reader prevents identification. The manual’s diagnostic process compares output with the device connected and disconnected.
Database recovery
Calibre backs up each book’s metadata in an OPF file inside the book folder. Library Maintenance can use those files to rebuild metadata.db after corruption. That recovery depends on the book folders still being intact. If an external drive receives another drive letter, the interface may open an empty library because it looks at the wrong path; Switch/create library points it back to the folder that contains metadata.db.
Moving collections
A library backup must include the complete library folder and all its subfolders. Copying only metadata.db loses the actual books, while copying only the book folders loses the central index and saved library structure. Calibre can switch among multiple libraries and copy or move selected books between them. The manual advises against a live library on a network drive because network filesystems can lack locking and link behavior that the database expects. Two processes writing to the same shared library can damage it.
