Cyrillic characters changed to question marks after save and close

Хиатална херния. ГЕРБ. Релаксация на диафрагмата. Вродени и продибити хернии…odt (15.9 KB)

File was created in a designated folder and typed in Bulgarian. I didn’t mess with the encoding settins, just went typing. After I saved it as .odt and reopened it it was messed up. I added a few cyrillic characters later and they’re displayed correctly.
Is it salvageable?
Thank you.

Welcome!
Unfortunately, it is not possible to return the contents - you will have to type the text again.
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All your Bulgarian text has turned into U+0037 QUESTION MARK. This is likely the result of using a text editor and saving the file as plain text in a non-Unicode encoding like some variant of ISO-8859, excluding ISO-8859-5. The file was later opened with Writer or inserted in a LO document (as suggested by Preformatted Text paragraph style).

Since original data has disappeared, you must retype it.