Before us is Mishnah 4 in the first chapter of Maseches Gittin. This Mishnah explains that there is a shared halachah - and in fact several halachos - that govern both the laws of gittei nashim, the bill of divorce, and the document that frees a non-Jewish slave or maidservant.
The words of the Mishnah:
"Echad gittei nashim v'echad shichrurei avadim shavu l'molich u'l'meivi" - these two types of documents are equated with one another in everything connected to the laws of one who brings and one who carries, that is, transporting the document from place to place.
The two types of documents:
A get - a bill of divorce given to a woman.
A shtar shichrur - the document that frees a Canaanite slave.
The halachos common to both:
Making the declaration: One who brings the document from overseas, or who carries it overseas - in either of the two directions - is required to make the declaration at the time he hands over the document.
The status of the messenger: The single messenger, through this statement of his, is considered as one who has the status of two witnesses.
The practical difference: if the husband comes along, or in the case of the document of freedom, the master, and claims that the document is a forgery, we pay no attention to his claim. For the statement of the messenger is considered the testimony of two witnesses, and a person cannot challenge it. This law applies equally to the bill of divorce and to the document of freedom alike.
In summary: This is one of the ways in which gittei nashim and shichrurei avadim share common halachos: the law of one who carries and one who brings, making the declaration in both directions, and the status of the single messenger as two witnesses - which removes the claim of forgery.