Document verification guides

How to recognise a forged document, which technical signals to look at, and what an automated check can and cannot prove. Each guide answers one question.

Individuals and rental files

How to verify a proof of address

Utility, telecom and internet bills used as proof of address: the technical checks that reveal an edited document, and when the checks simply cannot apply.

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How to verify a pay slip

Fake pay slips in rental files and loan applications: payroll software fingerprints, arithmetic checks and the French 2D-Doc barcode that expose an edited document.

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How to verify a French tax notice (avis d'imposition)

Landlord or agency: verify a tenant's French income-tax notice with the tax office's online service (SVAIR), the signed 2D-Doc code and the other documents in the file.

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Businesses and suppliers

How to spot a tampered invoice

Edited amounts, altered dates, swapped bank details: the technical evidence that gives away a tampered invoice PDF, and how to check for it.

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How to spot a fake IBAN on an invoice

Payment redirection fraud swaps the bank details on a genuine invoice. IBAN checksum, bank-code consistency and PDF tampering traces: how to check details received by email.

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Supplier bank-detail change fraud: verifying a new IBAN

A supplier announces new bank details? How the fraud works, the warning signs in the message and in the attached document, and the checks to run before you pay.

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How to verify a Kbis extract (French company registration)

Check a Kbis against the public registers (SIREN, directors, registered office, company status), spot a forged PDF, and know what a genuine Kbis does not prove.

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How to verify an URSSAF vigilance certificate (France)

Checking a French subcontractor's attestation de vigilance: the 15-character security code on urssaf.fr, the six-month validity, and what the law requires of the client.

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Method and technique

How to tell if a PDF was modified

A PDF keeps a record of its successive saves: incremental revisions, ghost objects, two sets of metadata. Where to look to find out whether a file was edited.

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2D-Doc: verifying French official documents

The 2D-Doc barcode on tax notices, pay slips and official certificates: what it contains, what it actually proves, and why it is different from every other check.

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Free tools

A single number to check rather than a whole document? These tools validate the check digits of an IBAN, a SIRET, a SIREN, a French VAT number or a French social security number right in your browser.

IBAN checker: validate the check digits and the length

Free IBAN checker: validates the mod-97 check digits, the expected length for the country and, for French IBANs, the RIB key. Everything runs in your browser.

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SIRET checker: Luhn check digit and the La Poste rule

Free SIRET checker: validates the 14-digit French establishment number with the Luhn formula, including the special rule for La Poste establishments. Runs locally.

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SIREN checker: Luhn check and matching French VAT number

Free SIREN checker: validates the 9-digit French company number with the Luhn formula and derives the intra-EU VAT number it implies. Runs in your browser, nothing is sent.

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French VAT number checker: key and SIREN consistency

Free French VAT number checker: validates the two-digit key against the SIREN it precedes and the SIREN's own Luhn digit. Runs in your browser; use VIES for registration.

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French social security number (NIR) key checker

Check the two-digit key of a French social security number (13 digits plus key, Corsica's 2A/2B included). The number stays in your browser: nothing is sent anywhere.

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Frequently asked questions

How does TrustyFile work?
Upload a PDF: it is analysed automatically by more than a dozen detection modules, and every signal found goes into an evidence ledger that produces a trust score from 0 to 100, with the list of anomalies and an explanation of each.
What exactly does TrustyFile check?
PDF metadata (producer software, dates, online converters), date and amount consistency, fonts, embedded images (pasting, resolution, EXIF), the file's internal structure (successive revisions, deleted objects, JavaScript), hidden or covered text, 2D-Doc barcodes and their signature, and company identifiers (SIRET, SIREN, VAT, IBAN).
Does TrustyFile store my documents?
No. Your document is processed temporarily, for the duration of the analysis, and is not retained. Only the file hash and company identifiers (SIRET, VAT) may be sent to verification APIs (INSEE, VIES, VirusTotal).
Can TrustyFile certify that a document is authentic?
No. TrustyFile is a decision-support tool, not a certification authority: it computes a risk score from technical indicators. A high score means few signs of manipulation but does not prove authenticity; a low score deserves a manual check. A scanned, flattened document yields little signal: in that case TrustyFile reports it as unverifiable rather than scoring it well by default.
Is TrustyFile free?
Yes, completely free, with no registration.
Which formats and limits?
PDF files only, up to 10 MB and 20 pages.

These guides describe the method. To apply it to a document, TrustyFile runs these checks automatically and for free.

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