or drop a file anywhere here
Files other than PDF are converted first. Signing in raises the size limit.
A certificate signature is a digital signature made with a cryptographic certificate and stored inside the PDF, which lets a PDF reader tell whether the file changed after it was signed. On this page you add one PDF, fill in Signer name, Reason and Location if you want them recorded, and select Run Certificate Sign. indox signs the file with a certificate kept on its own servers and returns a signed copy. The signature is invisible, so nothing is drawn on the pages. You cannot upload your own certificate or private key, which means the certificate belongs to indox and the signer name is an unverified label. The tools catalog marks Certificate Sign with the pro badge.
The page has no upload for a certificate or a key file, so one PDF is all you add. indox signs with a certificate stored on its servers. If none from a certificate authority is configured there, the signing service generates a self-signed one and uses that.
Three optional text boxes feed the signature: Signer name, Reason and Location. An empty Signer name or Location is filled in as indox, and an empty Reason becomes Signed by indox.
The signature is invisible. indox tells its signing engine not to draw a signature box, so no page gains a stamp, an image or a line of text.
If the signing service cannot be reached or rejects the PDF, the job stops and the page shows Couldn’t process file with the reason. No Download button appears for an unsigned copy.
Drop the file on the box marked Drop a file here, or select Choose file and pick the PDF from your device.
Type a Signer name, a Reason and a Location if you want them stored in the signature. All three boxes are optional, and Output format stays on PDF.
Select Run Certificate Sign and wait for the progress bar. When Conversion complete appears, choose Download to save the signed PDF.
You do not need a certificate of your own to use this page, because indox signs with one it already holds. That choice also sets the limit of what the signature says: it shows that the file was signed through indox and lets a reader see whether it changed afterward, and it does not vouch for you as a person. The signature stays off the page, so every page looks the same before and after. Your PDF reaches indox over HTTPS, and a failed signing job gives you a message instead of a file.
| What you see | Why | What to do |
|---|---|---|
| The reader says the signer is not trusted | A self-signed certificate is not issued by an authority the reader trusts | This is expected. The signature still shows whether the file changed. For identity checks by others, sign with a certificate from a certificate authority outside indox. |
| You see no signature on the page | The signature is invisible by design | Open the signature panel of your PDF reader. |
| The signature shows as broken | A tool rewrote the file after signing, and that includes Protect PDF and Change Permissions | Make signing the last step, and sign a clean copy again. |
| The job refuses a protected PDF | A signature cannot be applied to an encrypted file | Remove the password with Unlock PDF and sign the open copy. |
| You only need a time marker | Certificate signing records a signer, not a trusted time | Use Timestamp PDF. |
You have an approved report and want any later edit to be detectable. Sign the final PDF and share the signed copy.
Your app or workflow has to handle documents that carry a certificate signature. Sign a sample here to get a file with a real signature field.
You distribute price lists, statements or policies as PDFs. A signed copy lets a recipient's PDF reader show whether the file was altered after indox signed it.
Facts checked on October 16, 2026
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The certificate belongs to indox. It is either one that indox has configured on its servers or, when none is configured, a self-signed certificate that the signing service generates.
No. The page takes one PDF and three optional text values, and it has no field for a certificate or a key file.
No. The signature is stored in the file without a visible box. Open the signature panel of your PDF reader to see it.
A reader trusts a signature only when it trusts the certificate behind it. A self-signed certificate is not on a reader's trust list, so the reader warns about the signer while it can still check the file for changes.
They are written into the signature as text that a PDF reader can display. indox does not verify them, and a box left empty falls back to a default that names indox.
Not on this page. A signature cannot be applied to an encrypted file, so remove the password with Unlock PDF and sign the unlocked copy.
Any tool that rewrites the file breaks the signature, and that includes Protect PDF and Change Permissions. Make signing the last step.
In the tools catalog, Certificate Sign carries the pro badge, and the catalog filter lists that group as Pro / Dashboard. See the pricing page for what each plan includes.