Is the above grammatically correct?
1)
エッセイ mostly refers to a category of literature, not a concrete paper/book.
2)
液体 is not wrong, but I recommend a more common word for an example such like コーヒー, お茶 or 水.
Thus, there is no problem with, for instance, 彼は彼女の書類にコーヒーをこぼした。.
I have problem converting it into passive voice.
Could you please point out my mistakes? Thanks!
彼女のエッセイは彼に液体を零された。
The subject of a direct passive sentence is the object of the active sentence. Thus, it's コーヒー in this case. Note when the subject is inanimate, the agent is often omitted or hardly to say. If it's necessary to say, によって or から is used to indicate it.
彼によってコーヒーが彼女の書類にこぼされた。
If the indirect object is animate, another direct passive is possible.
e.g.
active: 彼は彼女にスピーチを頼んだ。
direct passive 1: 彼から彼女にスピーチが頼まれた。
direct passive 2: 彼女は彼に/からスピーチを頼まれた。
active: 彼は彼女にマイクを渡した。
direct passive 1: 彼から彼女にマイクが渡された。
direct passive 2: 彼女は彼に/からマイクを渡された。
As for your (or my?) example, 書類 is not "indirect object" in the first place. It's the target of the action just like 壁に石を投げる or 机の上に本を置く. 書類 is inanimate, so even if 書類 is the indirect object, it's impossible to make a direct passive sentence whose subject is 書類, anyway.
I try to make a suffering passive version as well.
I understand this does not always have a nuance of adversity as Toritoribe-san explained on
the other thread.
彼女は彼にエッセイが液体を零された。
彼女は彼にエッセイを液体で零された。
書類 is her property, thus, if the subject of the passive sentence is 彼女, that's possessor's passive. It doesn't always have "suffering" nuance. Anyway, you don't seem to understand what the subject and object are in the original active sentence, and how those words should be changed to (i.e., what particle should be attached to) in the adversative passive sentence. Try again.