Immutability is an essential feature of legally compliant and audit-proof archiving. This principle states that a document may no longer be changed, manipulated or deleted once it has been archived. This requirement is anchored in the GoBD and ensures that all tax-relevant documents and records are stored in their original form. To ensure that they cannot be changed, many companies rely on special archiving systems and document management systems (DMS) that have appropriate protection mechanisms. These include functions such as freezing documents, logging all access and changes and assigning access rights. An audit-proof archive must also ensure that every change or versioning of a document is traceable. The immutability of documents is particularly important when it comes to compliance with legal regulations and audits by authorities. It creates trust and ensures that the archived information can be used as evidence at any time.