How to sign a contract from your phone in 2026

The shift: from printable PDF to a contract you sign on your phone

Five years ago, signing a contract meant: print, find a blue pen, scan the document, email it back and store the physical copy in a drawer. In 2026 that flow has collapsed for two simple reasons: 78% of web traffic in Spain is mobile (Statcounter April 2026) and most people no longer own a printer.

The alternative is not "more complicated with technology." It is actually simpler: a unique link on WhatsApp, you open it on your phone, fill the fields, sign with your finger and both parties keep the same signed PDF. No app, no account, no printing. What changes is understanding what makes that signature legally weighty and which mistakes turn it into wet paper.

What you need and what you do NOT need

What you need: a phone with a camera and a connection (any model from the last 8 years works), the link to the contract and 2-3 minutes. That is all.

What you do NOT need (despite what some service providers claim): the FNMT digital certificate, an activated electronic ID, a specific app installed, a user account or a paid subscription. For the vast majority of private contracts between individuals, the simple electronic signature(digital handwritten signature + timestamp + document hash) regulated by EU Regulation 910/2014 (eIDAS) is enough.

Step 1 — Open the link on your phone

The other party (your landlord, your client, your car buyer) creates the contract on a platform like Runican and sends you a unique link by WhatsApp or email. Something like: runican.com/formulario/abc123…

Practical tip: always open the link from your browser, not from the WhatsApp WebView. If you open it inside WhatsApp on Android, some features (camera for ID, saving PDF to Files) may fail. Tap the three dots top right and pick "Open in browser".

Step 2 — Review the preview before signing anything

The contract loads with your data highlighted in colour. Read it carefully. Check: your full name, correct ID number(a single wrong digit invalidates the document before tax authorities), exact amount, dates and deadlines. If any field is missing or wrong, do not sign — contact the other party to fix it.

If the contract is long, the preview has a reading progress bar. Reaching the end is not mandatory, but signing without reading is like signing in blank — legally valid but case law (Spanish Supreme Court 2024) has begun to factor in lack of understanding in abusive clauses, especially with consumers.

Step 3 — Sign with your finger (yes, it works)

In 2026, the digital handwritten signature (the one you draw with your finger on the screen) has full validity as a simple electronic signature under art. 3.10 of the eIDAS Regulation. It is not the same as a qualified signature (which requires FNMT digital certificate or activated electronic ID), but for contracts between individuals it is enough in 95% of cases.

The signature is captured using a library like signature_pad that stores not only the image but also the pressure, speed and timing of the stroke. That enables later forensic handwriting analysis if anyone denies having signed. For probative value, the platform must bind the signature to the document via SHA-256 hash and timestamp.

Practical tip: rotate your phone to landscape for a more comfortable signing area. And sign the way you sign on paper — no need to be an artist. If you make a mistake, there is a"Clear" button; you can redo as many times as you want.

Step 4 — Upload your ID photo (if the other party requests it)

For contracts of certain value (leases, loans, vehicle sales), the other party may ask for a photo of the front and back of your ID. This does NOT replace the signature — it accompanies it as reinforced identity proof.

Important privacy warning: a serious platform must strip EXIF metadata (including geolocation) from the image before storing it. If you upload on a site that does not, your GPS location at the time of the photo stays embedded. Runican applies EXIF stripping automatically before saving (GDPR compliance).

Step 5 — Receive the signed PDF with verification QR

After tapping "Sign", within seconds you receive the final PDF. Three key elements:

• Digital handwritten signature from both parties, inserted as image in its proper spot.
• SHA-256 hash printed at the foot of the document. If anyone modifies a single letter of the PDF, the hash changes and the tampering becomes detectable.
• Verification QR code linking to a public page (runican.com/verificar/...) where anyone can check the document is intact and has not been tampered with.

Save the PDF in your Documents folder (iPhone: Share → Save to Files; Android: normal download). Both parties keep an identical copy with the same hash. In case of future dispute, the QR proves which version is the original signed one.

How to share it from your phone

The phone lets you share the PDF directly via the Web Share API: you tap the "Share" button, pick WhatsApp, email, AirDrop, Telegram or whatever you use, and the attached PDF is sent (not an expiring link). This matters in professional contexts: the recipient gets the full document, not dependent on your server.

If you need to send the contract to an accountant or lawyer, the signed PDF is fully compatible with any document system (Adobe Acrobat, Foxit, Apple Books, Google Drive). No special apps are needed to view or verify it — the standard phone camera scans the QR.

Honest take on legal validity

Here is what many services do not tell you clearly: the digital handwritten signature (finger drawing) is a simple electronic signature in the eIDAS classification. It has full validity for the vast majority of private contracts between individuals (leases, loans, NDAs, freelance contracts, sales of movable goods). It works as evidence in court and is admitted by Spanish tribunals (Supreme Court rulings since 2018 confirming arts. 326 of the Civil Procedure Act and 17 of Act 6/2020).

What it is NOT: a qualified electronic signature. For notarial deeds, mortgages, real estate gifts or telematic filings with the Spanish tax agency you need an FNMT certificate, an activated electronic ID or an accredited qualified trust service provider (TSP). That is not done by finger drawing — it requires reinforced identification and specific devices.

Rule of thumb: if the amount or risk is very high (real estate sale, mortgage, inheritance), go to a notary. For almost everything else, the digital handwritten signature + hash + QR is more than enough and cuts 90% of time and cost.

Common mistakes when signing from your phone

Mistake 1: signing before reviewing the full preview. Take the 60 seconds.

Mistake 2: not saving the PDF on your phone thinking "it is already in the cloud". Always save locally — links can expire.

Mistake 3: signing inside the WhatsApp WebView on Android (known camera and download issues). Always open in an external browser.

Mistake 4: using services without cryptographic hash or verification QR. Without those, the signed PDF can be tampered with leaving no trace.

Further reading

• What is a digital signature and when is it legally valid
• Contracts you should have before 30