An image or scan of an original document that had a physical black marker applied, might be possible to read using an image filter, if there are subtle differences in the color data where the text was, that might not be normally visible, but the image filter software might be able to highlight so it becomes visible. Probably not, but maybe.
If it’s some overblown word processor format that was designed without security in mind, like Microsoft Word, then the history of edits may be saved in the document. I’ve seen Word documents that include EVERYTHING EVER DONE TO THE DOCUMENT SINCE IT WAS CREATED, including earlier drafts or completely different letters or compositions, when the user took an existing document and re-used it to make later documents.