The lease arrives by email at 9 p.m. "Please sign and send back tonight." You're on your phone, there's no printer in sight, and the old routine — print, sign, scan, email — isn't happening.
The usual shortcut is an e-signature website or a "free PDF signer" app. Many of them want you to create an account, upload the contract to their servers, and sometimes pay before you can download the signed copy. For a document full of your name, address, income and signature, that's a lot to hand over just to add one scribble.
This guide shows how to sign a PDF in your phone's browser, with your finger, without uploading the file or installing anything.
Why sign locally
A signed agreement is one of the most sensitive files you own: it combines your identity, your signature and the terms you agreed to. When you sign through an online service, the document is uploaded and stored on their systems — sometimes indefinitely, as part of an "audit trail."
A client-side signer does the opposite. The web page loads a small PDF engine into your browser, opens the document from your phone's storage, lets you place your signature, and writes a new PDF — all on the device. Nothing is uploaded, there's no account, and it keeps working even in airplane mode once the page has loaded.
How LuniPDF's Sign PDF works
LuniPDF uses two open-source engines that run locally: PDF.js (from Mozilla) to show the pages on screen, and pdf-lib to write your signature into the file. It reads the document to find the signature lines, initial boxes and date blanks for each person, so you set up your signature once and then just tap Sign here ▶ to fill each spot in order. Anything it misses you can add anywhere with the ＋ toolbar. The tool handles landscape and rotated pages correctly, so the signature lands exactly where you placed it, the right way up.
Step-by-step on your phone
- Open the tool: lunibyte.com/lunipdf/sign-pdf.html in Safari (iPhone) or Chrome (Android).
- Choose the PDF. Tap the box. On iPhone, tap Browse to pick the file from the Files app — if it came by email, first save the attachment to Files. On Android, pick it from Downloads.
- Let it find the spots. LuniPDF reads the document and tells you how many signature, initials and date spots it found — for example "Found 19 signature, 85 initials and 16 date spots". If the form has several people (Landlord, Tenant…), pick who you are signing as.
- Set up once. Type your name, then draw your signature with your finger or tap Type to use your typed name. Your initials are made from your name — or tap Draw initials instead.
- Tap Start signing, then follow the yellow tags. The button says Sign here ▶, Initial here ▶ or Add date ▶ — each tap fills one spot and jumps to the next, like DocuSign. Missed a spot or need an extra one? Tap ＋ to add a signature, initials, date, text or a check mark anywhere. Tap a filled item to move, resize or remove it.
- Download. Tap Finish & download. The signed copy is saved as
yourfile-signed.pdf.
To send it, open the download (on iPhone, tap the download arrow in Safari's address bar), then use the Share button to attach it to an email or message.
On a computer
Exactly the same steps work with a mouse, trackpad or stylus — handy if you'd rather sign on a bigger screen.
Tips for a signature that looks right
- Turn your phone sideways before drawing. The wider box makes it much easier to write naturally.
- Write big, then shrink. A large signature drawn slowly looks smoother after you resize it on the page.
- Zoom out to check placement. Make sure the signature sits on the line, not over printed text.
- Keep the original. LuniPDF saves a new signed copy; your unsigned original stays untouched.
- Need the pages in a different order or a page removed first? Use Organize PDF before signing.
Before you send it back
A quick check saves an awkward "you missed a page" email later:
- Scroll through every page. Leases and contracts often need a signature on the last page and initials on earlier pages. Look for lines marked "Initial here" or "Tenant initials."
- Check names and dates. LuniPDF fills the date next to each signature line it finds. If the document also asks you to print your name or fill other blanks, tick Show blanks I can type in, or add text with ＋.
- Open the signed file once. Before attaching it, open
yourfile-signed.pdfand confirm every signature is where you expect it. - Rename it clearly, for example
lease-123-main-st-signed.pdf, so it's easy to find later. - Keep a copy for yourself. Save the signed PDF to Files (iPhone) or Drive/Downloads (Android) so you have your own record of exactly what you signed.
Is a finger-drawn signature legally valid?
In the United States, the federal ESIGN Act and the Uniform Electronic Transactions Act (adopted by almost every state) generally give electronic signatures the same legal effect as handwritten ones for most everyday agreements — leases, consent forms, offer letters, purchase agreements. Many other countries have similar laws.
There are exceptions. Wills, some real-estate deeds, court documents and certain official forms may require a wet-ink signature, a notary or a certified digital-signature service. If you're unsure, ask the person who sent you the document what they accept. This guide isn't legal advice.
How to confirm nothing was uploaded
On a computer, open your browser's developer tools (F12 → Network tab), clear the list, then sign and download. You'll see no request carrying your document. On a phone, the simplest test is to load the page, switch on airplane mode, and sign — it still works, because nothing needs to be sent.
Frequently asked questions
Can I sign more than one page? Yes. LuniPDF finds the spots on every page and takes you through them one by one; you can also add more with ＋. Each placement can be moved and resized on its own.
Will there be a watermark or a "signed with…" stamp? No. The signed PDF contains only your document and your signature.
Can I type my name instead of drawing? Yes. Tap Type during setup and your name is shown in a handwriting-style font (the exact font depends on your device). Your initials are made from your name automatically.
I spotted a mistake after downloading. What now? Your original PDF is unchanged, so just open it again in Sign PDF and place your signature afresh. Delete the incorrect signed copy so you don't send it by accident.
Is a drawn signature as secure as a "certified" digital signature? No — and it isn't meant to be. A drawn signature shows that you agreed, like ink on paper. Certificate-based digital signatures add cryptographic proof that the file hasn't changed since signing; some banks, governments and notaries require them. For everyday agreements, a drawn signature is what most senders expect.
Does it work offline? Yes, once the page has loaded.
How many times can I use it? Your first 3 uses are included — 3 in total across all LuniPDF tools, with no signup, no watermark. After that, LuniPDF Pro unlocks unlimited use of every tool.
Try it
Sign your next PDF on your phone, without uploading it anywhere: