Sign PDF and ZUGFeRD invoices remotely (PAdES) with SignPDFRemote

SDK members

LastError Licensekey

Code samples

VB.NET, C#, VB6 / VBScript (COM)

Published

2026-10-12

In short: With SignPDFRemote the Aloaha ZUGFeRD SDK (version 11.0.0.2 and later) signs a PDF – including a hybrid ZUGFeRD/Factur-X invoice – via the CodeB Remote Signature Service, part of the CodeB EUID Wallet software. The SDK sends the PDF to the service over HTTPS and receives it back with a PAdES signature (level B-B to B-LTA). No local certificate, smartcard or card reader is needed; signing also works unattended in batch jobs and from VB6/VBA via COM.

When to sign remotely?

• Servers and batch jobs: invoices are created and signed automatically without a certificate or card having to be installed on the server.
• Central key management: the signing key is held by the signing service, not on every workstation.
• Long-term verifiability: with level B-LTA the PDF contains timestamps and validation data for later verification.

CodeB EUID Wallet – now also for ZUGFeRD

The CodeB Remote Signature Service is part of the CodeB EUID Wallet software. The EUID Wallet is therefore now also used for ZUGFeRD: the Aloaha ZUGFeRD SDK (SignPDFRemote), the ZUGFeRD GUI, the PDF Viewer and the command-line tool zugcmd sign e-invoices directly via the EUID Wallet's signing service – without a certificate or smartcard on your own computer.

The software includes the CodeB Wallet – an EUDI wallet under eIDAS 2.0 for Android phones: identity data (PID), mobile driving licence, ID checks and PDF signing on the phone, advanced (AdES) via the signing service or qualified (QES) with the Maltese eID or a D-Trust card via NFC. All functions, video and access: CodeB Wallet – Aloaha's EU identity wallet and myeuid.app.

You do not need the app to sign invoices with the SDK: SignPDFRemote, the ZUGFeRD GUI, the PDF Viewer and zugcmd talk to the signing service directly, server to server.

Requirements

• Aloaha ZUGFeRD SDK version 11.0.0.2 or later with a valid licence.
• A user account on a production CodeB server (Remote Signature Service of the CodeB EUID Wallet); for the server-to-server call, sign-in with user name and password must be enabled for the tenant.

Important: https://phone.codeb.io is only CodeB's test server. It is suitable for trying things out but must not be used for production environments. For production you need your own CodeB server or tenant – contact us: info@aloaha.com. The examples therefore use the placeholder https://YOUR-CODEB-SERVER.

• Internet access via HTTPS from the calling computer to the signing service.
• The PDF is at most 10 MiB in size and not encrypted.

VB.NET

Dim LicenseKey As String = "YOUR-LICENCE-KEY"
Dim alo As New Aloaha_ZUGFeRD.XML(Aloaha_ZUGFeRD.iXML.ZUGFeRDProfile.comfort, False, LicenseKey)

' Arguments: input PDF, output ("" = replace input), your CodeB server, user, password,
' PAdES level, reason, location, contact, overwrite, licence, actual level (returned)
Dim level As String = ""
If alo.SignPDFRemote("C:\Rechnungen\RE-2026-0001_zugferd.pdf", "C:\Rechnungen\RE-2026-0001_signiert.pdf", _
                     "https://YOUR-CODEB-SERVER", "benutzer@firma.de", "YOUR-PASSWORD", "B-LTA", _
                     "Invoice approval", "Musterstadt", "", True, LicenseKey, level) Then
    Console.WriteLine("Signed, level: " & level)
Else
    Console.WriteLine("Error: " & alo.LastError)
End If

C#

var alo = new Aloaha_ZUGFeRD.XML();
alo.Licensekey = licenseKey;
string level = "";
bool ok = alo.SignPDFRemote(@"C:\Rechnungen\RE-2026-0001_zugferd.pdf", @"C:\Rechnungen\RE-2026-0001_signiert.pdf",
                            "https://YOUR-CODEB-SERVER", "benutzer@firma.de", "YOUR-PASSWORD",
                            "B-T", "Invoice approval", "Musterstadt", "", true, licenseKey, ref level);
Console.WriteLine(ok ? "Signed, level: " + level : "Error: " + alo.LastError);

VBA / VB6 (COM)

Dim alo As Object, level As String
Set alo = CreateObject("Aloaha_ZUGFeRD.XML")
alo.Licensekey = "YOUR-LICENCE-KEY"

If alo.SignPDFRemote("C:\Rechnungen\RE-2026-0001_zugferd.pdf", "C:\Rechnungen\RE-2026-0001_signiert.pdf", _
                     "https://YOUR-CODEB-SERVER", "benutzer@firma.de", "YOUR-PASSWORD", "B-LTA", _
                     "Invoice approval", "Musterstadt", "", True, "", level) Then
    Debug.Print "Signed, level: " & level
Else
    Debug.Print "Error: " & alo.LastError
End If

After updating to 11.0.0.2, re-register the type library so that COM clients see the new function.

Without files: SignPDFRemoteBytes

For web services and database applications, SignPDFRemoteBytes works directly with bytes and returns the signed PDF (or Nothing on error):

Dim signiert() As Byte = alo.SignPDFRemoteBytes(pdfBytes, "https://YOUR-CODEB-SERVER", "benutzer@firma.de", "YOUR-PASSWORD", "B-T")
If signiert Is Nothing Then Console.WriteLine(alo.LastError)

With a minimum level: the RemoteSigner class (from 11.0.0.3)

For servers and batch processing, version 11.0.0.3 and later provide a separate COM class Aloaha_ZUGFeRD.RemoteSigner. It signs just like SignPDFRemote (company seal via signDocBasic), but additionally offers:

• Minimum level (MinLevel, default B-B): if the service delivers a lower level, the signature counts as failed and no file is written.
• Reason for a downgrade (LevelNote) as well as requested and produced level (RequestedLevel, EffectiveLevel).
• Retry on rate limit (MaxRetries): on HTTP 429 the class waits for the time given by the service and tries again.
• Settings from the registry (LoadSettings) for servers: HKLM\Software\Aloaha\ZUGFeRD\CSC with BaseURL, User, PasswordProtected (encrypted for the machine with Windows DPAPI via ProtectPassword), Level, MinLevel, Reason, Location, Contact, TimeoutSeconds, MaxRetries.

Dim rs As New Aloaha_ZUGFeRD.RemoteSigner
rs.LicenseKey = "YOUR-LICENCE-KEY"
rs.ServerURL = "https://YOUR-CODEB-SERVER"
rs.UserName = "rechnungssiegel"
rs.Password = "YOUR-PASSWORD"
rs.Level = "B-LTA"
rs.MinLevel = "B-T"          ' no signing without a timestamp
rs.Reason = "Invoice approval"
rs.MaxRetries = 2            ' batch processing: on HTTP 429 wait and retry

If rs.SealFile("C:\Rechnungen\RE-2026-0001_zugferd.pdf", "C:\Rechnungen\RE-2026-0001_signiert.pdf") Then
    Console.WriteLine("Signed, level: " & rs.EffectiveLevel & " " & rs.LevelNote)
Else
    Console.WriteLine("Error: " & rs.LastError)
End If

From VBA/VB6: Set rs = CreateObject("Aloaha_ZUGFeRD.RemoteSigner"), then the same properties. The class does not follow redirects – user name and password are only sent to the configured server URL. The password is never output.

Signature levels (PAdES)

If the service cannot produce a higher level at the moment (e.g. because the time-stamping service is unreachable), it signs with the next lower level instead of aborting. The level actually produced is returned in the parameter EffectiveLevel (e.g. AdES-B-T). Always check it against your minimum requirement – most easily with RemoteSigner.MinLevel, the GUI setting minimum level or zugcmd -minlevel.

Signing a ZUGFeRD invoice: the order

1. Create the invoice data and save it as XML (quick start VB.NET).
2. Embed the XML into the PDF/A-3 with MergeXMLIntoPDF.
3. Sign with SignPDFRemote last. The signature is appended as an incremental update; the content and the embedded XML remain unchanged. Any later change to the PDF invalidates the signature.
4. In your tests, check the signed PDF with a PDF/A checker (e.g. veraPDF) and an e-invoice validator. B-LT adds a /DSS dictionary, B-LTA a document timestamp – both are permitted under PAdES.

Error handling

If the function returns False (or Nothing), the reason is in LastError. The password never appears in error messages.

Without programming: ZUGFeRD GUI, PDF Viewer and zugcmd

The same remote signing is built into the Aloaha ZUGFeRD GUI (tab Sign PDF) and the Aloaha ZUGFeRD PDF Viewer (Tools > Sign PDF / ZUGFeRD PDF) from version 11.0.0.2. Enter server URL, user, password and signature level once under signature settings; test connection checks the credentials with a test PDF; during signing a progress window shows that the service is working. From version 11.0.0.3 the command-line tool zugcmd also signs remotely (-remoteurl, -remoteuser, -remotepw, -level) – ideal for batch processing.

Legal framework

The CodeB Remote Signature Service creates advanced electronic signatures (AdES) within the meaning of the eIDAS Regulation, not qualified signatures (QES). Qualified signatures (QES) are only created with a qualified signature card such as the Maltese eID or the D-Trust Card 5.1 – in the CodeB Wallet via NFC on the phone. An electronic signature is not required for e-invoices in Germany; it does, however, provide verifiable proof of the authenticity and integrity of the document. Whether a validator displays the signature as "trusted" depends on whether it trusts the issuing certificate.

Technical background

The function uses the endpoint signatures/signDocBasic of the CSC v2 interface (Cloud Signature Consortium): an HTTPS POST with basic authentication, the PDF in the request, the signed PDF in the response. More about the service: Remote signatures at CodeB.