A method for file conversion that includes receiving a first file in a computer; wherein the first file is of a first format; wherein the computer has a memory having a boot sector, a quarantine sector and a non-quarantine sector; storing the first file at the quarantine sector; wherein the quarantine sector is isolated from the boot sector and the non-quarantine sector, where code in the quarantine sector is prevented from performing write actions on other memory sectors of the memory; checking whether the first file fulfills a set of criteria that comprise: (a) the first file is associated with a valid first digital signature that was generated by a first certificate authority and is of a known format; (b) the first file is about to be converted to a second file of a second format that supports digital signatures; and (c) the first file successfully passed at least one security check; converting the first file to the second file of the second format; generating, by a second certificate authority, a second digital signature of the second file when the first file fulfills the set of criteria; and storing the second file and the second digital signature at the non-quarantine sector.