Sign a PDF — Real Digital Signatures, Locally
Direct answer
Your certificate, your document and your password stay in this tab: a real RSA/SHA-256 signature is computed on your device and appended without touching the original bytes.
Your file never leaves this tab. No upload, no account, no signup, no email, no watermark — download the result the moment it's ready.
Verify it in 30 seconds- Signature
- PKCS#7 digitalnot an image
- Certificate
- .p12 / .pfxor generate self-signed
- File limit
- 50 MB
- Upload
- Nothingpassword stays on device
Drop a PDF to sign it
Up to 50 MB · your certificate and password stay on this device · the file is never uploaded
More ways to work
Choose another PDF task
Related tools from the BytesPDF directory.
Files are not transferred between tools. Select the document again on the next page; it is processed locally in your browser.
Honest limits
What Sign a PDF Does — and What It Refuses
The documents this tool will not touch, and the ten-second checks to run before you send the result.
Works on
What this tool handles reliably.
- Applies a real cryptographic signature, so a reader can detect later edits.
- Imports your .p12/.pfx certificate, or generates a self-signed identity locally.
- Keeps the document and the certificate password inside this browser tab.
Refuses on purpose
Not bugs — decisions we made and will state.
- To make a self-signed identity trusted by other people — that needs a CA-issued certificate.
- To obtain a new key for you: the .p12 it generates is the only copy, and losing it means losing the identity.
- To counter-sign or timestamp through a network authority.
Check afterwards
The ten seconds we ask you to spend.
- Download and store the .p12 backup before you close the tab.
- Open the signed file in a reader and inspect the signature panel.
- Expect a trust warning from readers for self-signed signatures — that is normal, not a failure.
Written for Sign a PDF specifically. If your file is on the refuses list, the page you need is the tool that handles it — not this one with the limits removed.
Step by step
How to Sign a PDF — Real Digital Signatures, Locally in 3 Easy Steps
Browser-local document processing with no application installation required.
Drop the PDF
Up to 50 MB. The file stays in this tab for the whole process.
Choose Your Identity
Import a .p12/.pfx certificate with its password, or generate a self-signed identity and download the .p12 backup.
Sign & Download
Add an optional reason and location, sign, and download the signed PDF — the original bytes are kept untouched as an incremental revision.
Capabilities
Why Use Our Sign a PDF — Real Digital Signatures, Locally Tool?
Current capabilities and limitations, described without universal quality or speed promises.
Real Cryptographic Signatures
RSA-2048 with SHA-256 in a PKCS#7 detached signature — the same format Acrobat uses. Any change to the file after signing breaks the signature visibly.
Your Certificate Never Leaves
Import your .p12/.pfx or create an identity here — the file, its password and the PDF are processed in this tab and uploaded to nobody.
Self-Signed With a Backup
No certificate yet? Generate one locally and download the .p12 backup — the only copy of your signing key, so keep it safe.
Reason & Location Recorded
Optionally record why you signed and from where — both are locked into the signed data and shown to whoever verifies the file.
FAQ
Frequently Asked Questions
Get clear answers about data flow, formatting, integrity, and usage limits.
How much does BytesPDF Pro signing cost?
Is this a real digital signature or just an image of my name?
Why does Adobe Acrobat say 'signature validity is unknown'?
What can I use a self-signed signature for?
What is a .p12 backup and why download it?
Does my certificate or password get uploaded?
Can I sign a PDF that already has a signature?
Can I sign a password-protected PDF, or an empty one?
Side by side
How BytesPDF Compares to Other Sign a PDF Tools
Most online PDF services process documents on remote servers. Here is how BytesPDF compares on data location, usage limits, and workflow fit.
Adobe Acrobat
When to choose them: You need desktop-level optimization controls, preflight, editing, or professional print workflows.
When to choose BytesPDF: You need one clear job done in a current browser, without sending PDF content to BytesPDF.
Server-based PDF tools
When to choose them: The job needs heavy OCR, large batches, collaboration, storage, or files bigger than a browser can hold.
When to choose BytesPDF: The operation you need runs locally, and keeping the document off a server matters.
Where your file goes
Others: Uploaded to remote cloud servers, processed there, and held during their retention window.
BytesPDF: Read and rewritten in this browser tab. 0 bytes are ever sent to BytesPDF servers.
Usage limits & quotas
Others: Daily task caps (Smallpdf: 2 tasks/day), processing queues, or subscription paywalls.
BytesPDF: No daily task quota, no account and no signup. Published file and device limits apply. Pro gates apply only to specialist workflows such as target-size compression, batch jobs, OCR and signatures.
What limits you
Others: The provider's commercial limits, upload caps, and subscription tiers.
BytesPDF: Your own device memory, published up front: 150 MB desktop, 50 MB mobile.
Platform & setup
Others: Web upload roundtrip or an OS-specific installer (e.g. PDF24 Creator on Windows).
BytesPDF: Runs in any modern browser on Mac, Windows, Linux, Chromebook, iPhone, and Android.
Directory
PDF Tool Directory
Browse free core tools and Pro workflows for compression, merging, OCR, signatures and more. PDF content stays in your browser.
Choose your next PDF task.
Selected PDF content for supported workflows is processed in your browser and is not uploaded to BytesPDF servers.
No account · No signup · No watermark · No PDF upload