Question: "Is that (parad) what they meant by fixed mercury?"
Original Answer: "Yes! You asked me a question about fixed mercury, I love you!"
Actual Answer with a working brain: Yes and no. Parad is the most literal form of fixed mercury as it is in fact metallic mercury in solid, purified, medicinal form. But the language of Alchemy is especially subtle in the West, and fixed mercury can mean a few things depending on weather we are talking of internal work or external lab work.
Energetically, in the Internal Work, Volatile Mercury is free life energy that hasn't been assimilated into a living form. It's said to be most concentrated in rainwater before it touches the earth, and mist/morning dew. Alchemists would funnel rain water off of tile roof tops, and hang out large sheets over fields to collect rain water and dew. The theory is that the sheets and tile are near energetically inert, and once they are saturated they can't collect any more life essence and thus the remaining dew/water is still full of primordial volatile mercury. Once the water touches rocks, soil, plants, people, animals, etc, it becomes fixed in that thing.
In Eastern Alchemical practice the Alchemist would rise early in the morning to breathe in the morning mist and assimilated life force directly that way since the morning mist has an enormous amount of life force within it, and through concentration it is quickly assimilated. Within animals mercury can be built up and volatilized in the saliva, sexual fluids, and blood, though it still is flavored to the animal/human kingdom. There are Indian and Taoist techniques that have made their way to the West where a skilled practitioner can give amazing fellatio, and consume the vital essence of their partner through swallowing ejaculate. It is also possible for this to be accomplished through cunnilingus if the practitioner can make their female partner ejaculate sufficiently.
In the Outer Work, Mercury is fixed in the natural alcohol of plants, as well as a type of "Metallic/Mineral Mercury" in metals and minerals. It is volatilized through combustion or maceration, etc, and then refixed in the final Alchemical product, and combined with either the Sulphur, Salt, or Sulphur and Salt of the materia.
In short, Fixed Mercury is the life essence of a kingdom (animal, vegetable, or mineral) bound to a specific thing within that kingdom by it's carrier agent, be it dew, semen, alcohol, etc.