Why signing a PDF is still so painful
PDF is a destination format. It exists so a document looks identical on every screen and every printer — which is exactly why it resists being changed. That's a feature right up until the document needs something from you: a signature, a date, a checked box. Then the format designed to be final becomes the obstacle, and most people fall back on the old ritual: print it, sign it with a pen, scan it or photograph it, and email the result back.
The common workarounds aren't much better. Pasting an image of your signature into a PDF editor produces a file that looks signed but proves almost nothing — there's no record of who placed that image, when, or whether the document changed afterward, and anyone holding the file can keep editing it. Desktop editors that do this cost money, and they still don't answer the harder question: how does the other person sign their half?
What you actually want is simpler. Open the PDF in a browser, put the fields where they belong, let everyone sign from whatever device they're holding, and end up with a locked file plus evidence of what happened. That's the flow this guide walks through, and on tuyaform it's free.
Step 1: Create a free account and upload your PDF
The people you send a document to never need an account — but the person preparing it does, and it's free. Sign up, create a new document from your dashboard, and instead of building it from scratch, upload the PDF you already have. Contracts, leases, NDAs, permission slips: if it's already written, there's no reason to rebuild it.
Uploads are PDF-only, up to 4 MB. If the document lives in Word or Google Docs, export it to PDF first — every word processor can. Once uploaded, each page renders in your browser exactly as your signers will see it, which matters for the next step: you'll place fields visually, on the real pages.
Step 2: Place fields visually, page by page
The builder shows your PDF page by page, and you drag fields directly onto the spots that need them. Two field types capture a mark: Signature and Initials. One fills itself: Date signed is stamped automatically at the moment of signing, so nobody backdates by accident. The rest collect the details agreements usually need — Full name, Email, Text for anything free-form, and Checkbox for an explicit "I agree."
Because you're placing fields on the rendered page rather than relying on the PDF's internal structure, this works with any PDF — including scans, where the "signature line" is just pixels. Drop the signature field onto the line on page four, resize it to fit, and put initials at the foot of each page if the agreement calls for it.
Every field is assigned to a specific signer, and the builder color-codes fields per signer so a two-party agreement stays legible: the tenant's fields in one color, the landlord's in another. Required fields must be completed before a signer can finish; optional ones can be left blank.
Step 3: Sign it yourself, send it out — or both
If you're the only one signing — the classic "fill and sign" case — add yourself as the signer, with your own email address. You'll open your own signing link, complete the fields you placed, and draw your signature with a finger or mouse, or type your name in a handwriting-style font.
If others need to sign, add each one by name and email. You can send invitations by email with a short message, choose whether people sign in sequence or all at once in parallel, and optionally protect a signer with an access code you share through a separate channel — a text message, not the same email. Or skip email entirely: tuyaform can generate the signing links for you to deliver yourself, over WhatsApp, Slack, or however you already talk.
Whoever receives it, the experience is the same: no account, no app, no download. The link opens the document in their browser — phone, tablet, or computer — with their fields highlighted. On the free plan, only emailed invitations are metered (30 per month); signing links you share yourself are unlimited.
What "sealed and tamper-evident" actually means
When the last signer finishes, tuyaform generates the final PDF with every signature and field value burned into the pages, then seals it by computing a SHA-256 hash of the file — a cryptographic fingerprint unique to those exact bytes. Change anything afterward — a digit in a payment amount, a name, a single character — and the file no longer matches its recorded fingerprint.
That's what tamper-evident means, and the precision matters: it doesn't make the file impossible to edit — no PDF is — it makes any edit provable. A document whose fingerprint still matches is demonstrably the exact document everyone signed. The seal travels with a Certificate of Completion and a full audit trail — who signed, when, from which email address and IP, in what order — and every party receives the completed, sealed PDF, so everyone holds the same evidence.
When a signature image is enough — and when it isn't
Not every signature needs a ceremony. If you're adding your mark to a school permission slip, a cover letter, or an internal memo nobody will ever dispute, a simple signature image is fine: draw or type it in an online signature maker — tuyaform has a free one — download the image, place it, done.
The dividing line is whether anyone could ever deny it. The moment money, obligations, or deadlines are involved — a freelance contract, a lease, a settlement — you want the audit trail: proof of who signed, when, and that the document hasn't changed since. A pasted image proves none of that; a sealed PDF with a Certificate of Completion proves all of it. When in doubt, use the full flow — it costs the same: nothing.
Is it legally valid? Plus tips for real-world PDFs
In broad strokes, yes: electronic signatures are recognized in most of the world. In the US, the ESIGN Act and UETA say a signature can't be denied legal effect merely because it's electronic; the EU's eIDAS regulation does the same. What courts look for is intent to sign, consent to transact electronically, attribution to the right person, and an unaltered record — precisely the things an audit trail and a seal support. A few categories, like wills or documents requiring a notary, follow their own rules, and this is general education rather than legal advice; our guide on e-signature legality covers the frameworks in depth.
A few practical tips from real usage. Scanned PDFs work fine — you're placing fields on the visible page, so it doesn't matter that a scan is "just an image" — but straighten the scan and check its legibility before uploading, because that's exactly what your signers will read. Page order is preserved as uploaded, so fix a jumbled document at the source before you upload it. And if your signers are likely on phones, favor fewer, larger fields: signing works well in a phone browser, and a typed signature often looks cleaner than a finger-drawn one on a small screen.