Bom dia.
Você precisar criar um componente ACBrEAD e setar a chave nele e indicar para o ACBrPAF e ACBrECF.
abaixo segue um codigo de exemplo.
obs: não esqueça de trocar para sua chave RSA. voce pode criar usando o ACBrEAD.
ACBrEAD acbrEAD = new ACBrEAD();
acbrEAD.ChavePrivada = "-----BEGIN RSA PRIVATE KEY-----" +
"MIICXwIBAAKBgQC+TZjfcw/a/SovoqQPOW5bbKn4CQw4DeZJA3Y9vJrYHKN4aCQv" +
"z0i3AG9kGdsTSZdZ/clh4xv6tUwPsBdZJHrm21gH7wN/zKLTvXbs+i3x7U00ElCB" +
"YyZ8BOXJWVMuye0UvSz7p4JwSopugzbjaImIGy+5LvgcjUCn3OZzWpwYWQIDAQAB" +
"AoGBAKAycEtB8An37ghVkGfkf7rkmZxb+XZCdSXnjSThXTQpv46/lB7PDrZG3n5U" +
"qa/t1kQCOQF3DnmZHqNiJ/V5mR7ApbciQj4WYVLkMCgltru3MmzIUQ9IiLtAgaCv" +
"uHc0MAzt/OWgQ93uFnLf4ubp4+2PTHiiIChv2m78s605wX2lAkEA+3pPsPdXcaOe" +
"7T7C4hn1qg93ksN96UutB1APF3YAjWVWuPwzZv4hExiMPc0uKvVK2H3tP4P5CkM5" +
"YMIEGEkF2wJBAMG5qmoYksz+MFZ2cd7gt68mf3Oq9F59qkHHcoV+1ttXx5pfzwat" +
"kelhKkN+LV1XsgS0bGAKu2NitOMBUAcnItsCQQCEJxqJ3PFO/rUd58VyHEJFRCuK" +
"LMGWP/aFyUSlB5XyuDaCr8YzcYjgCB5qu9BvMshKTKLIpgnRotIcTtjoCjfRAkEA" +
"tsqHn+Bb9A0McykDvPdwmlXLAMsYFWihk7urtYa/GOw0rNcmMvjnqrxB8rlF+MNc" +
"d8/+SokV02s5ntCIQJeO7QJBAKp2BCOIck+uhMPDiw/1788yQLD6mVb/pBzClzBn" +
"pTMAFPGJG2fO4YJn/pUHdtDtSenX8TibWve+gY6oFCFw/Ts="+
"-----END RSA PRIVATE KEY-----";
AcbrECF.EAD = acbrEAD;
AcbrPAF.EAD = acbrEAD;
AcbrPAF.SaveFileTXT_P(acbrPAFRegistroP1, acbrPAFRegistroP2, "Mercadorias.txt");
AcbrECF.PafMF_LMFS_Espelho(dataDe, dataAte, tbArquivo.Text);
Att.
Rafael Dias.