Baba Metzia 1:6-7

Baba Metzia 1:6

If one found papers documenting a financial obligation that includes a lien on someone’s property, he should not return them to the lender because the court will make the borrower pay based on these papers (and the finder doesn’t know if the debt may have already been paid). If they do not include a lien on someone’s property, he should return them to the lender because the court will not make the borrower pay based on these papers (and therefore the doubt as to whether or not the debt may already have been paid is immaterial). This is Rabbi Meir’s opinion; the Sages say that the finder should never return the papers because the court will always use them to make the borrower pay.

Baba Metzia 1:7

If a person found documents of divorce, or for freeing servants, or last wills, or granting gifts, or receipts, he should not return them to the intended recipients because the possibility always exists that the person who had them written changed his mind before delivering them.