What does an archive timestamp add to a signed PDF?

The third tick box under Long-term proof in the Digital Signature tool is "Add an archive timestamp". It is off by default, and most people do not need it. Here is who does.

What is already in place before it

By this point you have, in order:

1. The signature: proof the document has not changed and who signed it.
2. [A trusted timestamp](/blog/what-is-a-trusted-timestamp-on-a-signed-pdf): proof of when the signature was made.
3. [Long-term validation](/blog/what-long-term-validation-ltv-means): the certificates and cancellation checks, packed into the file so it can be judged later without the internet.

That is already a strong file. So what is left?

The gap it closes

Step 3 stores evidence. But that evidence was added after signing, and it is not itself covered by the original signature. In a hundred-year archive, someone eventually asks the awkward question: *how do we know that evidence is the original evidence, and not something swapped in later?*

The archive timestamp answers it. It wraps a fresh, independent timestamp around everything (the document, the signature, the first timestamp, and the stored evidence) and says: all of this existed together, exactly like this, on this date.

The everyday version

Think of a box of papers going into a records office.

• The signature is the signed contract inside.
• The trusted timestamp is the date stamp on the contract.
• Long-term validation is the supporting paperwork you put in the box alongside it.
• The archive timestamp is the records office sealing the whole box and writing the date across the seal.

Break the seal and everyone can see. Nothing inside can be quietly replaced.

Why it needs the other two

The tick box is greyed out until long-term validation is on, which in turn needs the trusted timestamp. The tool's hint says it directly: "Seals the whole file, including the validation data, for archiving. Needs long-term validation."

There is no point sealing a box that has nothing in it to protect.

Who actually needs it

Turn it on for:

• documents going into a long-term archive: deeds, permits, court filings, medical or academic records,
• anything you are told must follow a formal archiving rule, often described as B-LTA or "long-term archival",
• files you genuinely expect to be reopened in twenty or thirty years.

Leave it off for:

• ordinary contracts and offer letters,
• invoices and approvals,
• anything where five to ten years of proof is more than enough.

What it does not do

It does not make your signature more valid. It does not add anything about who you are. It does not change whether a reader shows a green tick. It is purely about keeping the whole package provably intact over a very long time.

What happens if the attempt fails

Timestamping the finished file means one more call to an independent service. If that call fails, the tool does not quietly carry on and let you think it worked. The result page shows either "An archive timestamp seals the whole file, including the validation data" or "The archive timestamp was not added."

Your document is still signed either way. You simply know exactly what you have.

Can I add one to a file that is already signed?

Yes. In principle, an archive timestamp is a seal over a file, not a signature by a person, so it can be added to a finished document. In the Digital Signature tool it is applied as part of the signing you are doing now, at the end of the same run.

How to see whether a file has one

In Verify PDF Signature, a document timestamp shows up as its own entry in the list of signatures, and the PAdES level noted beside a signature moves up to B-LTA when everything is in place.