Export/Import Digital Signature

Hi at all... i would like to export my digital signature from my Acrobat Reader but i saw a strange behavior...When a go to Preference->Signature->Identities e Trsut Certificate and i do the procedure for to export, i have the possibility to export signature on fdf, p7c or cer file... when i try to create a new signature and i choose import a file, the only possibility that i have is p12 or pfx file... Now, why the export is same type of file and import another type? If i export my signature is because i want after to import in another computer right? How can i export the signature in right format?

Thanks