Copyright law operates to protect proprietory software developers' rights to limit use of their software. The protection granted to them as creators of the work under the law is based in United States, for example, on the United States law governing computer programs, much of which is codified in the Copyright Act of 1976
This law operates by protecting software companies, mostly growing out of the United States jurisdiction, who effectively license users to use the software in accordance with copyright law, with no ownership of the software itself granted. Further, to implement Digital Restrictions Management, their licenses restrict the usage of their software.
Digital Restrictions Management (better known as Digital Rights Management) is a technique that is applied by companies for some file formats, i.e to prohibit users from opening "proprietary file formats" in other software.
It is also accompanied by contractual or license restrictions that limit users from accessing the content in such files and from sharing it "illegally".
This technique was traditionally made for content which is used in distribution channels for example, Adobe Digital Editions prevents file owners from accessing .acsm files and it is used for implementing DRM in publishers' contracts with libraries with restrictions imposed on their patrons on copying or distributing copies.
A natural consequence of restricting users from accessing published content is to also disallow interoperability which can remove the lock on the digital content itself. While Adobe uses DRM in its distribution channel, many others utilise it to limit the interoperability of their software products and works made using those products.
Legal treatment of DRM and interoperability
The Digital Millenium Copyright Act "criminalizes the production and distribution of technology that tries to circumvent DRM.". However, as regards interoperability, the Act itself provides an exception under which computer programmers are allowed to reverse engineer a DRM product to provide for interoperability.
What this means for you is, regardless of the software licensing terms, you are still entitled to break the DRM lock for the purposes of achieving interoperability as holding otherwise would defeat public policy in the United States, considering that,
In Vault Corp. v. Quaid Software Ltd, Louisiana Software License Enforcement Act clause permitting the Copyright owner to restrict or prohibit software decompilation or disassembly was barred by the Copyright Act and therefore was held unenforceable by the US Courts.
SaaS and Users' rights
For example, this is the case with Apple Media's Services Terms and Conditions' "Usage Terms" which states the following (this sub-clause is incorporated in its non-media services also, including the text-editor known as "Pages"):
You may access our Services only using Apple’s software, and may not modify or use modified versions of such software.
In such a case, restriction operates on the basis of contract law governing contracts of service, whereby the service provider and you have agreed to provision of this service on certain restrictive terms and conditions.