How to digitally sign a PDF with a certificate: a step-by-step guide

更新日期：2026年10月2日

本指南尚未提供繁體中文版，因此以英文顯示。工具本身支援繁體中文。

A picture of a signature only shows that someone put it there. A digital signature is part of the file: any reader can check that the document hasn't changed since it was signed, and who signed it. Digitally Sign PDF signs with your own certificate - the .p12 or .pfx file your provider gave you - or with one made in your browser. The certificate and its key never leave the tab; nothing is uploaded.

免註冊即可免費試用：你的檔案不會離開你的裝置。

開啟PDF 數位簽章

重點摘要

Drop your PDFs on the page, or press Add files.
Open your certificate with its password - or make one under Create one.
Fill in the details and choose whether the signature shows on the page.
Press Sign: the signed file is saved to your device straight away.

Add the files

Drop the PDFs anywhere on the page, or press Add files. The selected document opens large in the middle; every page is shown, one under the other. A document that is already signed can take another signature - the earlier ones stay valid, because the new one is added after them.

Digitally Sign PDF with three files: the lease agreement open, the rail's Certificate section waiting for a certificate

The certificate

My certificate - choose your .p12 or .pfx file and type its password. The key stays in this browser tab only: nothing is uploaded or stored, and a reload forgets it.
Create one - type your name (and an e-mail or organisation if you like), and a certificate is made in your browser. Save it as a password-protected .p12 file to sign with the same certificate next time.

A certificate made in the browser: issued to Jordan Ellis, self-signed, valid for three years, with the option to save it as a .p12 file

A certificate you made yourself is self-signed: a reader confirms the document is unchanged, but shows the signer as not verified, since anyone can make one in any name. For a signature others must trust, use a certificate from a provider.

Details, appearance and certification

Details - a reason ("I approve this document"), a place and a contact; readers show them with the signature. All optional.
Appearance - Invisible (the signature is listed in the reader's signature panel) or On the page: a box with your name, the date and the reason, placed where you click; drag it to move, pull its corner to resize. You can add a handwritten signature to the box.
Certification - as the document's first signature you can also certify it and state what others may change afterwards: nothing, filling in forms and signing, or comments as well.

The signature placed on page 1: a box reading Digitally signed by Jordan Ellis, with the date and the reason — The visible signature: your name, the date and the reason, wherever you click.

Sign and save

Press Sign (or Certify and sign). The signed file is saved to your device at once - several together as a ZIP. The file isn't rewritten: the signature is appended to it, so everything that was there stays exactly as it was.

Check the result with Verify PDF Signature. Only need your handwritten signature on the page, with no certificate? Use Sign PDF.

Limits

Without an account, and with a free one, you can sign two files in a run, each up to 15 MB. With Pro there is no limit on the number or the size, and you can save your settings (never the certificate) as a preset. A password-protected document has to be unlocked with Unlock PDF first.

What next?

Check a signature? Verify PDF Signature.
A signature picture only? Sign PDF.
Fill in a form before signing? Fill PDF forms.

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