The phrase "in a separate document" is correct and usable in written English.
You can use it when referring to a piece of writing which is not included within the same text as the one you are writing. For example: "All the supporting evidence for my argument can be found in a separate document".
In a separate document, Regan typed up the steps for decrypting the letter.
In a separate document, the European Commission granted that such an emergency already obtained in the UK.
In a separate document unsealed today, the Justice Department agreed earlier this week to provide Mr. Moussaoui with the videotape.
In a separate document, Mr Wood is asked: "Do you admit the adultery alleged in the petition?" He replies: "Yes".
In a separate document Winehouse was asked: "Do you admit the adultery alleged in the petition?" The star answered: "Yes".
Often, the creator of a trust outlines his or her philosophy in a separate document, to avoid having it construed as legally binding.
In others, the agreement could be a separate document that basically gives each property owner the right to use the other's property.
A separate document contained in the apparent file dump appears to show Sudan, along with Russia, listed as "not officially supported", as opposed to the "active" or "expired" status held by most other nation states.
Indeed, a separate document, prepared in question-and-answer form about the guidelines, states no fewer than three times that the Reform rabbinate "is not targeting anyone" for conversion.
A separate document, the Service Standard Guideline was developed in an attempt to operationalize the ECD Policy Framework.
In a separate internal document, leaked to Guardian Australia, it is revealed IHMS was failing to act on complaints of asylum seekers including accusations of bullying.
