diff --git a/marshal.go b/marshal.go
new file mode 100644
index 0000000..e94339b
--- /dev/null
+++ b/marshal.go
@@ -0,0 +1,25 @@
+package pkcs7
+
+import "encoding/asn1"
+
+func (p7 *PKCS7) Marshal() ([]byte, error) {
+	var contentType asn1.ObjectIdentifier
+	switch p7.raw.(type) {
+	case signedData:
+		contentType = OIDSignedData
+	case envelopedData:
+		contentType = OIDEnvelopedData
+	case encryptedData:
+		contentType = OIDEncryptedData
+	default:
+		return nil, ErrUnsupportedContentType
+	}
+	inner, err := asn1.Marshal(p7.raw)
+	if err != nil {
+		return nil, err
+	}
+	return asn1.Marshal(contentInfo{
+		ContentType: contentType,
+		Content:     asn1.RawValue{Class: 2, Tag: 0, Bytes: inner, IsCompound: true},
+	})
+}
diff --git a/marshal_test.go b/marshal_test.go
new file mode 100644
index 0000000..204b450
--- /dev/null
+++ b/marshal_test.go
@@ -0,0 +1,60 @@
+package pkcs7
+
+import (
+	"bytes"
+	"crypto/x509"
+	"encoding/pem"
+	"os"
+	"testing"
+)
+
+func TestPKCS7_Marshal(t *testing.T) {
+	content := []byte("Hello World")
+	rootCert, err := createTestCertificateByIssuer("PKCS7 Test Root CA", nil, x509.SHA256WithRSA, true)
+	if err != nil {
+		t.Fatalf("cannot generate root cert: %s", err)
+	}
+	truststore := x509.NewCertPool()
+	truststore.AddCert(rootCert.Certificate)
+	signerCert, err := createTestCertificateByIssuer("PKCS7 Test Signer Cert", rootCert, x509.SHA256WithRSA, false)
+	if err != nil {
+		t.Fatalf("cannot generate signer cert: %s", err)
+	}
+	toBeSigned, err := NewSignedData(content)
+	if err != nil {
+		t.Fatalf("cannot initialize signed data: %s", err)
+	}
+
+	// Set the digest to match the end entity cert
+	signerDigest, _ := getDigestOIDForSignatureAlgorithm(signerCert.Certificate.SignatureAlgorithm)
+	toBeSigned.SetDigestAlgorithm(signerDigest)
+
+	if err := toBeSigned.AddSignerChain(signerCert.Certificate, *signerCert.PrivateKey, nil, SignerInfoConfig{}); err != nil {
+		t.Fatalf("cannot add signer: %s", err)
+	}
+	signed, err := toBeSigned.Finish()
+	if err != nil {
+		t.Fatalf("cannot finish signing data: %s", err)
+	}
+	pem.Encode(os.Stdout, &pem.Block{Type: "PKCS7", Bytes: signed})
+
+	p7, err := Parse(signed)
+	if err != nil {
+		t.Fatalf("cannot parse signed data: %s", err)
+	}
+
+	marshaled, err := p7.Marshal()
+	if err != nil {
+		t.Fatalf("cannot marshal signed data: %s", err)
+	}
+	p7Reparsed, err := Parse(marshaled)
+	if err != nil {
+		t.Fatalf("cannot reparse signed data: %s", err)
+	}
+	if !bytes.Equal(p7.Content, p7Reparsed.Content) {
+		t.Errorf("content was not found in the reparsed data:\n\tExpected: %s\n\tActual: %s", p7.Content, p7Reparsed.Content)
+	}
+	if err := p7Reparsed.VerifyWithChain(truststore); err != nil {
+		t.Errorf("cannot verify reparsed data: %s", err)
+	}
+}
diff --git a/sign.go b/sign.go
index eb07f30..8ecc18d 100644
--- a/sign.go
+++ b/sign.go
@@ -23,9 +23,9 @@ type SignedData struct {
 	encryptionOid       asn1.ObjectIdentifier
 }
 
-// Copy creates a new SignedData struct based on existing PKCS7 signed data.
-func Copy(data *PKCS7, unauthenticatedAttrs ...Attribute) ([]byte, error) {
-	rawData, isSignedData := data.raw.(signedData)
+// CopyWithUnsignedAttributes creates a copy of the PKCS7 struct with different unsigned attributes.
+func (p7 *PKCS7) CopyWithUnsignedAttributes(unauthenticatedAttrs ...Attribute) (*PKCS7, error) {
+	rawData, isSignedData := p7.raw.(signedData)
 	if !isSignedData {
 		return nil, ErrUnsupportedContentType
 	}
@@ -38,15 +38,17 @@ func Copy(data *PKCS7, unauthenticatedAttrs ...Attribute) ([]byte, error) {
 			return nil, err
 		}
 	}
-	inner, err := asn1.Marshal(rawData)
+	certs, err := rawData.Certificates.Parse()
 	if err != nil {
 		return nil, err
 	}
-	outer := contentInfo{
-		ContentType: OIDSignedData,
-		Content:     asn1.RawValue{Class: 2, Tag: 0, Bytes: inner, IsCompound: true},
-	}
-	return asn1.Marshal(outer)
+	return &PKCS7{
+		Content:      p7.Content,
+		Certificates: certs,
+		CRLs:         rawData.CRLs,
+		Signers:      rawData.SignerInfos,
+		raw:          rawData,
+	}, nil
 }
 
 // NewSignedData takes data and initializes a PKCS7 SignedData struct that is
diff --git a/sign_test.go b/sign_test.go
index 65e544d..ee1a2c4 100644
--- a/sign_test.go
+++ b/sign_test.go
@@ -265,7 +265,7 @@ func fromHex(s string) *big.Int {
 	return result
 }
 
-func TestCopy(t *testing.T) {
+func TestCopyWithUnsignedAttributes(t *testing.T) {
 	content := []byte("Hello World")
 	rootCert, err := createTestCertificateByIssuer("PKCS7 Test Root CA", nil, x509.SHA256WithRSA, true)
 	if err != nil {
@@ -301,17 +301,13 @@ func TestCopy(t *testing.T) {
 	}
 	testOid := asn1.ObjectIdentifier{2, 3, 4, 5, 6, 7}
 	testValue := "TestValue"
-	copied, err := Copy(p7, Attribute{
+	p7, err = p7.CopyWithUnsignedAttributes(Attribute{
 		Type:  testOid,
 		Value: testValue,
 	})
 	if err != nil {
 		t.Fatalf("cannot copy signed data: %s", err)
 	}
-	p7, err = Parse(copied)
-	if err != nil {
-		t.Fatalf("cannot parse copied data: %s", err)
-	}
 
 	if !bytes.Equal(content, p7.Content) {
 		t.Errorf("content was not found in the copied data:\n\tExpected: %s\n\tActual: %s", content, p7.Content)