Add a certificate-based digital signature to a PDF, inspect a PKCS#12 certificate, or check a PDF’s signed bytes. These operations use our conversion server. Signing and certificate inspection upload the certificate, including its private key, and its password; only use material you are authorized to share with this service.
How to sign with a certificate
- Keep an unsigned original and open the Certificate tab. Select your .p12 or .pfx file and enter its password. Selecting the file alone does not upload it.
- Use Load and inspect certificate if you want to read the included subject, issuer and validity dates. This is a server upload, not a local inspection or a certificate trust check.
- Switch to Sign and select your PDF. Add a reason and optional location. Use a simple, unencrypted source; some PDF structures, including compressed object streams, are not supported by the signing engine.
- Select Sign PDF and download. This uploads the PDF, certificate and certificate password. Open the downloaded file in a trusted PDF reader and check its signature panel and trust result before relying on it.
A digital signature is not a drawn signature
A digital signature uses the private key in your certificate to sign document bytes. This tool does not draw handwriting or place a visible signature image on a chosen page. It does not create, issue or renew certificates.
Certificate details describe the certificate file; they do not establish that its issuer is trusted or that the person named is who you expect. A self-signed certificate can produce intact signed bytes while remaining untrusted in a reader.
This workflow is intended for a single signature on an unsigned source. It does not provide trusted timestamping, long-term validation or a workflow that preserves a chain of existing signatures. Complete all other PDF edits before signing.
How to interpret Verify results
Choose Verify and select a PDF, then run Verify PDF signatures. Verification uploads the PDF but does not need your private certificate. It checks supported signature byte ranges, up to the first 32 found.
Signed bytes intact means the cryptographic check passed for those bytes. Modified means the signed revision was intact but the file contains later changes not covered by it. Invalid means validation failed; unverified means the signature structure was unsupported, malformed or could not be checked.
This check does not validate the certificate trust chain, revocation, the signer’s identity or whether the certificate is acceptable for your purpose. No supported signature found does not rule out unsupported structures or a visible signature image. Use a trusted PDF reader for a fuller assessment.
Private keys, uploads and compatibility
A PKCS#12 file can contain a private signing key. Uploading it allows the service to use that key for the requested operation. Do not upload organizational or personal certificates whose handling rules prohibit sharing them with a hosted service; use your approved local signing workflow instead.
The hosted limits are currently 5 MB per PDF and 1 MB per certificate; development configurations may differ. Keep the tab open during processing and read the retention policy before proceeding.
If signing fails, check the certificate password and PDF compatibility. Converting an important signed or encrypted document just to make it load can change its meaning or invalidate existing signatures. Use a suitable unsigned source or another approved signing application for complex documents.
Frequently asked questions
Does a successful verification prove the signer is trusted?
No. This service checks signed-byte integrity. It does not check certificate trust, revocation or the signer’s identity, even if it displays the certificate subject and validity dates.
Is my certificate processed only in the browser?
No. Inspecting or signing uploads the certificate, including its private key, and its password to the conversion server. Merely choosing the file or entering the password does not trigger that upload.
Can I use this to add a handwritten signature image?
No. This page performs certificate-based signing and signature checks. It does not offer a drawing pad or signature-image placement.