How long to keep signed contracts and their evidence

Keep the sealed PDF and its evidence pack at least as long as the underlying transaction can still be disputed. For routine commercial agreements that means at least the applicable limitation period, which varies by jurisdiction; in the US, federal tax rules give concrete numbers worth knowing: IRS Publication 583 sets three years from filing as the general period, six years if income was understated by more than 25 percent, seven years for bad-debt or worthless-securities claims, and at least four years for employment tax records.

The safe pattern is simple: when a number in a dispute runs on a clock, keep the evidence past the clock.

The final sealed PDF — not a printout, not a screenshot, not a forward's attachment. The value is in the file's own evidence: the PAdES signature, the trusted timestamp, and the sealed evidence certificate with its hash-chained audit trail. A printout is a picture of the evidence; the PDF is the evidence.

Alongside it: the delivery email's verification code (or the code printed inside the evidence certificate), so a counterparty can verify without asking you to prove anything.

In the US, ESIGN §7001(d) provides that electronic records satisfy retention requirements if they accurately reflect the information and remain accessible to all persons entitled to see it — the law explicitly blesses keeping records in electronic form. In the EU, no general eIDAS rule imposes a retention period for electronic signatures; the drivers are national limitation periods, tax law and sector rules, so the jurisdictional check is local.

The failure mode of long retention is not storage — it is decay of the proof. Certificates expire; the OCSP responders and CRL distributors that let a validator check revocation are switched off; hash algorithms age out. A B-T signature gets thinner every year; B-LT embeds the validation data in the PDF so validation does not depend on outside services; B-LTA re-seals with archival timestamps before the algorithms age out.

So when you choose where signed documents live, ask the question that matters at year seven: can someone still verify this file, with no help from the vendor? If the answer comes from the file itself — as it does with B-LT and above — retention is a storage task. If not, the evidence is quietly rotting while the documents look fine.