The Peruzbal process:
Before the Shemitah year begins the lender is to gather a valid court of three Kosher Jews [see Halacha 6] and state to them “I hereby hand to you all the debts that are owed to me [and through doing so] I should be allowed to collect them whenever I desire.” [Alternatively one is to write and sign a document including the above words and hand it to the tribunal of judges. A Rav can join another two Kosher Jews and prepare the Peruzbal document and then have people place their signature on it. See Q&A regarding the verbal method versus the document method.]
Is it proper to write the Peruzbal rather than simply recite the statement to the court?
One is not required to do so as stated above, and so is the custom of many Jews even initially to rely on the verbal Peruzbal. Nevertheless there are many Jews that are scrupulous to sign a document which is handed to the Beis Din. The Rebbe encouraged the distribution of Peruzbal documents by a Beis Din. One of the advantageous of doing the Peruzbal through a document of a Beis Din is regarding that if the borrower does not have any land the Beis Din can facilitate the acquiring of land on his behalf. See Halacha 5 for further details on this subject!
The Hebrew Nussach:
“הריני מוסר לכם כל חובות שיש לי שאגבה אותם כל זמן שארצה“
May one appoint a messenger to perform the Peruzbal on his behalf in presence of a valid court?
 Admur 35; Likkutei Sichos 7/355; 24/316; See Q&A!
 This method contains numerous advantages over the oral method as explained next regarding acquiring land to the borrower. [Likkutei Sichos 24/316]
The original institution of the Peruzbal was in a document form, in which the loaner would write on a document that he is handing all of his debts to the court and the court or witnesses would sign on it. [Gittin 36a; Rambam 9/18; Michaber 37/19] However this only applied for non-Torah scholars. However Torah scholars were not required to write a Peruzbal document and rather a mere statement sufficed. [Rambam 9/27 based on Gittin 37a; Michaber 67/20] Others however rule that this leniency applies for all people and not just for Torah scholars, and hence anyone can choose to simply recite the Peruzbal words rather than write a Peruzbal document. [Tur 67; Rama 67/20; Admur 35; Likkutei Sichos 7/355; 24/316; See Nitei Gavriel p. 299]
 As rules Admur 35; Likkutei Sichos 7/355; 24/316; See Nitei Gavriel p. 299
 See Nitei Gavriel p. 299 that so is the custom of many Jerusalem G-d fearing Jews, and so I was told by Harav Asher Lemel Hakohen.
 Rav Avraham Chaim Naah writes to say the Nussach and then have the Beis Din write a document affirming the Peruzbal. [Yagdil Torah 25 p. 78] Ben Ish Chaiy Ki Savo 26 states that he wrote a “Shetar Peruzbal” and distributed it to people of the city.
 Likkutei Sichos 24/316
 Admur 35
 See Rama 67/20; Nitei Gavriel 28/1 and Poskim mentioned in footnote 1; However see there for Poskim that argue; Rav Avraham Chaim Naah [brought in Yagdil Torah 25 p. 78] writes that he initiated in 1924 that the Beis Din of Jerusalem [Rav Yosef Chaim Zonnenfeld] appoint a Shliach to go around and sign people on a document that states that they are appointing him as their Shliach to give the Peruzbal to the court. This person would then read the Nussach of the Peruzbal on their behalf in front of the court.