A CTZ file is a document created by Cherrytree, a note-taking application. It stores document data, which may include text, tables, objects, and images, compressed with Zip compression. CTZ files are protected with a password and cannot be viewed without the password entered.

Users typically save Cherrytree documents as .CTB files but if they protect them with a password, the documents are saved as .CTX files. Cherrytree users may also save documents in XML format as .CTD files. Password-protected CTD files are saved as CTZ files. CTD and CTZ files are useful for saving documents that are smaller in size than CTB and CTX files. CTZ files are commonly opened by Cherrytree, but they may also be opened by 7-Zip in Windows. If a user opens it in 7-Zip, the password must still be entered before the file can be opened. NOTE: Cherrytree is developed by giuspen, a portmanteau of Giuseppe Penone.