FP Sign: Check and store signed documents
What you receive once a signing process is complete, how to check its validity, and how to file the document correctly.
Introduction
Once the final signature has been added, FP Sign sends the signed document as a PDF file and a workflow report to all parties involved. This completes the process. What happens to the file afterwards is up to you; this article explains how to verify the signature and file the document so that it is retained as evidence.
First, a few clarifications, as there are often misunderstandings regarding signed documents: the signature is embedded in the PDF file, not in the visible signature image. Although a printout shows the image, the signature itself can no longer be verified on it.
A signed PDF must not be edited after it has been signed. Any change – including a comment added afterwards or saving the file using a different tool – will invalidate the signature.
You do not need to verify the signature to use the document. Verification is a way of confirming its validity for yourself, for example before passing the document on to third parties.
What you will receive upon completion
The completion email from FP Sign contains two attachments.
The signed PDF is the actual document. It contains all signatures as embedded PAdES signatures, as well as the visible signature images. This file is the original; it must be retained.
The workflow report documents the process: who signed and when, what type of signature was used and, where applicable, whether an SMS TAN was entered. The report is linked to the document via a hash value and confirms that the two belong together.
With an FP Sign account, you can download both files again at any time under ‘Received requests’ > ‘Signed requests’. If you do not have an account, you can request them from us if they are lost; we archive every signed document.
The workflow report contains only evidence of the process. The legally valid signature is contained within the PDF file itself and can be verified even without the report.
Verifying the signature in a PDF reader
The signature can be verified in any PDF programme capable of validating eIDAS signatures. The most widely used is the free Adobe Acrobat Reader. Other programmes display signatures in a similar way; the terminology may vary.
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Open the signed PDF in Acrobat Reader
When you open the file, the Reader automatically verifies the signatures. A banner displaying the result appears at the top of the document.
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Read the banner
A green tick with the text ‘Signed and all signatures are valid’ means: the document has not been altered since it was signed, and the certificate is trustworthy. A yellow warning symbol indicates a problem, such as an unknown certificate.
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View the signature properties
Clicking on a signature and then on ‘Signature Properties’ displays the certificate, the issuer and the time of signing. There you can also see whether the Reader classifies the certificate as trustworthy.
What a yellow warning icon means
A yellow icon does not mean that the document has been tampered with. In most cases, the reader does not recognise the issuer’s certificate and therefore classifies it as ‘unknown’. The signature itself is intact; the document has not been altered.
This occurs more frequently with advanced signatures, as their certificates are not included in the EU Trusted List. A red icon or the message “Document was modified after signing”, on the other hand, indicates a genuine problem; in this case, please contact us.
Verification on a smartphone
On Android and iOS, the verification options are limited. Many mobile PDF apps display the signature image but do not provide validation. For a reliable verification, please use Acrobat Reader on a computer.
Why printing invalidates the signature
The signature is a digital fingerprint of the document, encrypted using the signatory’s certificate. It exists only within the file. A printout displays the signature image and the text, but no longer contains a verifiable signature.
If a printout is later scanned back in, a new file without a signature is created. Legally, this is merely a copy and can no longer be verified for integrity.
A digitally signed document loses its evidential value if it is printed out and scanned back in, or saved again using a PDF tool. Always keep the unaltered original file from the confirmation email.
Merging with other PDFs, rotating pages or adding comments is also considered a modification. If you need a signed document in a different format, work with a copy and keep the original unchanged.
Retention
The same retention periods apply as for paper documents. You must retain contracts, powers of attorney and tax-relevant documents for as long as required by commercial and tax law. The responsibility for this lies with you as a business; we also archive the document in your file.
Digitally signed PDFs are suitable for GoBD-compliant archiving. The signature makes subsequent changes detectable, and the PDF format ensures readability over long periods. You do not need a separate archiving system for this; an organised storage location with a backup copy is usually sufficient.
What happens to expired certificates
Signature certificates have a limited validity period. A signature that was valid at the time of signing remains valid even after the certificate has expired. The embedded timestamp records when the signature was applied.
Acrobat Reader may display a warning icon for expired certificates. This does not affect the validity of the signature at the time it was created. For very long retention periods, there are procedures for re-signing; this is not necessary for standard retention periods.
Common sources of error
- Printed and filed away, file deleted: A printed copy is not a verifiable signature. Without the file, proof is missing; it must then be requested from us.
- PDF ‘cleaned’ and saved again after signing: Saving the file under a new name using a different PDF tool may remove the signature or render it invalid. The original file remains unchanged.
- Signed PDF merged with other documents: Merging creates a new file without a valid signature. Merged collections are working copies, not the original.
- Yellow warning icon interpreted as a forgery: In most cases, this simply means that the reader does not recognise the certificate. The document remains unchanged. Only an indication of changes made after the signature is a problem.
- Workflow report filed as the original: The report documents the process but is not the signed document. Both files should be filed together.
Frequently asked questions
Do I need to print out the signed document and file it away?
No. The PDF file is the original. A printout may be useful as a reference copy, but it does not replace the file.
How long do I need to keep the document?
For as long as you would keep a comparable paper document. For tax-related documents, the retention periods under commercial and tax law apply. If you are unsure, please contact us.
Acrobat Reader is displaying a yellow icon. Is the document invalid?
Usually not. The icon usually means that Acrobat Reader does not recognise the certificate as trustworthy. As long as there is no indication of changes made after the document was signed, the document remains unchanged.
I’ve lost the confirmation email. How can I get hold of the document?
If you have an FP Sign account, you can download it again under ‘Signed Requests’. If you do not have an account, please contact us; the document is in your file.
Can I pass the signed PDF on to third parties, such as a bank?
Yes. The signature is embedded in the PDF and can be verified by the recipient in exactly the same way. Please send the unaltered file, not a printout or a scan.
Can I make additions to a signed document at a later date?
No, not without invalidating the signature. Additions must be made as a separate document, which must also be signed. Please contact us if a change is required.
Can the signed PDF be archived in accordance with GoBD?
Yes. The signature makes subsequent changes detectable, and the PDF format is readable in the long term. This is provided that the file is stored unchanged and in a retrievable format.
What is the difference between a workflow report and an audit report?
The workflow report describes the sequence of the entire process. The audit report, also known as a verification log, confirms for a single signing step that the document remains unchanged. Both are available in the FP Sign account.
Legal notice
This article provides an overview and is not a substitute for individual advice. The functionality and interface of FP Sign and PDF programmes may change as a result of updates. Retention periods depend on the specific document and the applicable regulations.
If you have specific questions regarding the retention of a particular document or a verification result, please contact us directly.
Last updated: September 2026