If you need to convert files from one markup format into another, pandoc is your swiss-army knife.

Encrypt Dropbox, Google Drive, and any other cloud. Cryptomator is free and open source.

VeraCrypt is free open-source disk encryption software for Windows, Mac OS X and Linux. In case an attacker forces you to reveal the password, VeraCrypt provides plausible deniability. In contrast to file encryption, data encryption performed by VeraCrypt is real-time (on-the-fly), automatic, transparent, needs very little memory, and does not involve temporary unencrypted files.