The Advantages of Plaintext
The linux information project defines plaintext as:
"...a term used in crytography that refers to a message before encryption or after decryption. That is, it is a message in a form that is easily readable by humans."
This human readability is wherein lies the value of plaintext: it is non-proprietary, easy to search, and easy to vectorize (or publish and disseminate).
Plaintext is the most malleable and accessible textual resource possible.
If vectors are unified by plaintext, then e-books, PDFs, personal papers, etc. each become searchable at once. A successful union of vectors would happen at points of origin, so no retroactive decryption or change of format is necessary. Instead of documents being born as Word documents, we might instead start them as plaintext. A movement to Word might then be an act of publication rather than composition.
Once form and content are separated in this way, the user or composer is afforded certain freedoms: the formatting layer in Word, for example, is proprietary. That is, an italicized word is encrypted by private code that needs to be purchased in order to be made readable by humans.
Markdown, for instance, is a style of plaintext whose formatting is based on plaintext. Rather than encrypting text into italics, markdown incorporates readable textual elements (e.g. word) that can be formatted in italics (or bold, all caps, etc.) later if need be.
An operating system like Unix is based on plaintext data because it is extremely sustainable. If you keep documents in plaintext data, it can be incorporated anywhere—say, a library. Plaintext has greater longevity than other formats.
Plaintext is easy to mine for info as well, for doing full-text searchs.
If you want to work programmatically, Adobe won't allow for it, as its files are encrypted and not accessible through the back end. Encryption restricts low-level access to files.
To appoint a certain encrypted format as the standard is to buy into a single model and to make it almost a law. Use of plaintext ensures the most democratic format possible.