Gemara

108b (Mishnah #1): If Reuven stole from his father, swore falsely to him, and his father died, he pays principal and Chomesh to his (Rashi - father's; Tosfos - own) children or brothers, and brings an Asham.

(Really, since he inherits his father, some (or all) of the payments should revert to him. However, he must remove the entire theft from his Reshus.) If he does not want (or lacks the money) to pay the share he should inherit, he borrows this amount, and the creditors collect it from his share of the inheritance.

(Rav Yosef): (If one stole from his father, and he knows of no other heirs to give it to,) he must get rid of the theft. He may even give it to Tzedakah.

(Rav Papa): He must say 'this is what I stole from my father.'

Question: Why can't he keep the money? He can pardon himself!

(Mishnah #2): If the owner pardoned the thief from paying the principal (the thief need not travel to return what he owes).

This shows that the theft can be pardoned!

Answer #1 (R. Yochanan): Mishnah #2 is like R. Yosi ha'Glili, who holds that theft can be pardoned. Mishnah #1 is like R. Akiva, who holds that it cannot be pardoned.

(Beraisa - R. Yosi ha'Glili): Reuven stole from a convert and swore falsely to him, and heard that the convert died. He was taking the money to give to the Kohanim, and met the convert on the way. If the convert agreed that the theft be like a loan, and he died, Reuven keeps the money.

R. Akiva says, he may not keep the theft.

Summation of answer: They argue about whether theft can be pardoned. No one distinguishes pardoning oneself or pardoning another!

Objection (Rav Sheshes): If so, R. Yosi should teach that a thief can pardon himself (and all the more so another), and R. Akiva should teach that one cannot pardon another (and all the more so, himself)!

Answer #2 (Rav Sheshes): Both Mishnayos are like R. Yosi. One can pardon only another, but he cannot pardon himself. In the Beraisa, the thief keeps the money because it was converted to a loan.

Answer #3 (Rabah): Both Mishnayos are like R. Akiva. One cannot pardon himself, but he can pardon others.

Question: This implies that R. Yosi holds that one can pardon even himself. If so, when did the Torah obligate to give Gezel ha'Ger (what was stolen from a convert who later died) to Kohanim? (He can pardon himself!)

Answer (Rava): He stole from a convert, swore, and admitted after the convert died. When he admits, Hash-m acquires the theft (for the Kohanim).

Kesuvos 81b (Beraisa): Reuven owed money to his brother Levi. Levi died and his wife fell to Yibum. Reuven cannot say 'since I inherit, the money will stay by me.' Rather, we take the money, buy land with it, and he eats the Peros.

85b: A relative of Rav Nachman sold collection rights to her Kesuvah. She was divorced, and then died. The buyer came to collect from her daughter.

Rav Nachman: She can pardon her father's obligation to pay her mother's Kesuvah (and then she will inherit that money from her father)!

Rishonim

Ramban (Sefer ha'Zechus Kesuvos 40b DH u'Batel): The case of the Yavam merely teaches that seizure does not exempt him. Indeed, according to Shmuel he can pardon to himself, and is liable due to Garmi. Or, perhaps we learn from here that one cannot pardon to himself, for there is a lien on the property. Pardon to oneself does not uproot the lien mid'Oraisa, and not mid'Rabanan. If a woman sold her Kesuvah and died, her son who inherits his father cannot pardon to himself.

Rambam (Hilchos Gezeilah 8:4): If one stole from a convert, swore, then admitted and converted the obligation to a loan (set a date for payment) and then the convert died, even though he merits that the theft belongs to him, he must remove it from his possession.

Ra'avad: This is like R. Akiva.

Rambam (5): This is when he admitted. If one stole from a convert, swore to him, and then the convert died, he must pay principal and Chomesh to Kohanim of the Mishmar, brings an Asham and gets atonement.

Ra'avad: Even if he admitted, if he did not convert the obligation to a loan, he must give everything to Kohanim according to R. Akiva. The Gemara said differently only according to R. Yosi ha'Glili.

Magid Mishneh: The Rambam explains that converting the obligation to a loan does not help according to either Tana. R. Yosi ha'Glili always holds that he keeps it, and R. Akiva says that it suffices to remove it from his possession, but he need not give it to Kohanim.

Mishneh l'Melech: R. Yosi ha'Glili holds that even if if he did not convert it to a loan, he can pardon to himself and acquire. The Gemara asked how Gezel ha'Ger applies according to him! The Ra'avad holds that R. Akiva's law is only when he converted it to a loan.

Rosh (Kesuvos 9:10): Rashi explains that Rav Nachman's relative sold her Kesuvah, and the buyer claimed from her daughter, who came to collect her mother's Kesuvah from her father. This is difficult. Surely, when her mother sold her Kesuvah, she gave the document to the buyer and wrote him a sale document. Her father will pay only one who will return the Kesuvah document to him! Rather, also her father died, and she was the only heir. We learn that even in such a case that it was initially hers, she can pardon to her father and acquire in place of him. The Gemara in Bava Kama similarly asked that one who stole from a convert should be able to pardon to himself.

Beis Yosef (DH Kosav Ba'al ha'Terumos): Sefer ha'Terumos (51:6:6) explains like Rashi. We do not learn about pardoning to oneself from the daughter. We learn only from Bava Kama. Only R. Yosi says that one can pardon himself. The Halachah follows R. Akiva. The Rambam rules like R. Akiva. The Ramban distinguishes. In Bava Kama, he inherited his father's money. Here, his father sold the property, so the son cannot uproot the lien.

Poskim

Shulchan Aruch (CM 66:23): One who sold a loan document can pardon it. Even his heir can pardon it. However, an heir cannot pardon to himself to make the buyer lose. E.g. if Reuven lent to his son Levi in a document, and sold it to Shimon, and Reuven died, Levi cannot say 'since I inherit, I make Chazakah to pardon to myself. I need not pay due to Garmi, for I did not intend to hurt the buyer, rather, to exempt myself.' Rather, he pays the full debt to Shimon.

Gra (98): This is like Kesuvos 81b and R. Akiva. It explains Kesuvos 85b like Rashi (her father was alive).

SMA (59): If the heir could pardon to himself, he would be exempt, for he did not intend to hurt the buyer. However, he cannot, for he himself borrowed. He must pay the debt, even according to the opinion (in the Rema, Sa'if 32) that normally obligates paying only the money paid for it.

Shulchan Aruch (ibid): Some disagree and say that one can pardon even to himself.

Gra (100): This is like the Rosh, who says that her father died. It explains Kesuvos 81b like Tosfos (DH Lo. The Yavam could not pardon to himself, for he inherited only due to her. Or, the Tana holds like R. Meir, who obligates paying the full amount of the document due to Garmi, so he would not gain from this.) It holds that the Halachah follows R. Yosi ha'Glili. This is difficult. The Halachah follows R. Akiva against one colleague!

SMA (60): This opinion holds that he is like anyone else who pardons, even though he did not intend to harm. They argue about whether he pays the full debt, or the money he received.

Rebuttal (Shach 81): The Shulchan Aruch holds that this opinion totally exempts, since he did not intend to harm. Also the Bach says so. Sefer ha'Terumos brings the Ramban, but concludes that we obligate paying only when one intended to harm.

Shach (82): This opinion is primary. However, he must pay due to Garmi. One is liable for Garmi even without intent to harm. The buyer cannot be Toref Meshubadim (collect land that the heir sold), for the debt is not from when he bought, rather, from the time of pardon, so he is not Toref due to his document. Also, the heir is believed to say 'I paid you what I owe.' Also, if the heir was a minor, he is exempt even after he matures. If a married woman (inherited her father) and there was a loan document against him, she can pardon it and need not pay due to Garmi until she is widowed or divorced, for her husband acquires whatever she acquires. Shiltei ha'Giborim permits counseling an heir to pardon to help the heir. However, a judge should not do so.