Terms that come up in any conversation about signing.
Read about electronic signature for a while and the jargon piles up — partly legal, partly technical. This page explains the relevant terms in the context of Fdo. with short, practical definitions.
- Simple signature
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An image of your signature placed on a PDF, without a digital certificate or extra authentication. This is what Fdo. does.
It is valid in many private and commercial contexts (contracts between companies, quotes, internal certificates), but not the kind of signature public administrations require for online filings.
- Advanced electronic signature
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A signature uniquely linked to the signer, capable of identifying them, and created with means under their sole control (typically OTP via SMS, video identification or a cloud certificate).
Platforms like DocuSign, Signaturit or Adobe Sign typically offer advanced signature with a full audit trail. Useful when you need to record who signed, when, and from where.
- Qualified electronic signature
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An advanced signature made with a qualified certificate issued by a qualified trust service provider. It is legally equivalent to a handwritten signature.
It is the kind required for filings with public administrations (tax authority, social security, courts). It is performed using the official electronic-signature tool issued by the relevant government.
- eIDAS
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Regulation (EU) 910/2014 on electronic identification and trust services. It defines the three categories of electronic signature (simple, advanced and qualified) and harmonises their validity across the European Union.
Regulation (EU) 2024/1183 (Wallet) updates the framework and introduces the European Digital Identity Wallet.
- FNMT certificate
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Digital certificate issued by the Spanish Royal Mint (Fábrica Nacional de Moneda y Timbre). It identifies the holder — natural person, legal entity or representative — to the Spanish administration.
It is one of the certificates accepted by every public-administration portal in Spain. Issued after in-person identification at an authorised office.
- AutoFirma
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Free desktop application from the Spanish Government for signing documents with a digital certificate. Runs on Windows, macOS and Linux.
It is the standard tool for filings with public administrations. AutoFirma's bulk-signing mode does exist but is hard to find and forces the same template across the entire folder.
- LexNET
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Electronic court notification system run by the Spanish Ministry of Justice. Lawyers, court agents and other legal professionals receive and submit court documents through it using qualified electronic signature.
- Text anchoring
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An automatic signature-placement mode in Fdo. The app looks for a specific text inside the PDF (for example, "Signed:" or "The Director") and places the signature image on or near that text.
Useful when the PDFs in the batch are not identical but share the same signing template. If the anchor lands off on some PDF, the review tab lets you fix it.
- OCR
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Optical Character Recognition. A technology that turns images of text into selectable text.
If a PDF is a scan with no OCR layer, its content is just an image and text anchoring will not work. Fdo. detects it and warns you.
- localStorage
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Browser storage. Each website can save small amounts of data (a few MB) on the user's device.
Fdo. uses localStorage only when the user enables "remember signature": it stores the signature image so it is available in the next session. It is not sent to any server.
- WebAssembly (WASM)
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A portable binary format that runs in the browser at near-native speed. It allows code compiled from C, Rust or C++ to run alongside JavaScript.
Fdo. mostly uses JavaScript (pdf-lib and pdf.js). Some optimisations inside pdf.js use WASM internally, but it is not the critical path.
- pdf-lib
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Open-source JavaScript library for creating and modifying PDFs. Fdo. uses it to embed the signature image on each PDF.
Embedding the signature as a PDF object — rather than flattening it over the entire page — keeps the document light and editable.
- pdf.js
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Mozilla's library for rendering PDFs in the browser. It is the library Firefox uses internally to display the PDFs you open.
Fdo. uses it to render thumbnails and to let you see where the signature will land before applying it to the batch.
- DNIe
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The Spanish electronic National Identity card. It carries a qualified digital certificate that allows signing documents with the same legal validity as a handwritten signature.
To use it you need a card reader, or a phone with NFC and the latest version of the DNIe app.
- QTSP (qualified trust service provider)
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A supervised entity that issues qualified certificates and other trust services under the eIDAS Regulation (FNMT, Camerfirma, ACA, etc. in Spain).
- VALIDe
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Spanish central-government service for validating electronic signatures and certificates issued by recognised QTSPs.
Missing a term?
If you bump into one that isn't here, write to hola@fdo.app. If it's relevant, it gets added.