What is the difference between Digital Signature and Sign PDF?
Sign PDF
places a drawn, typed, or uploaded picture of your signature on the
page; it's visual only. This tool applies a cryptographic PKCS#7
signature using your X.509 certificate, so a PDF reader can verify
who signed and detect any change made afterward. You can also show a
visible signature block at the same time.
Can I sign with a PEM certificate instead of a .pfx or .p12 file?
Yes. Upload a single .pem file that contains both the certificate
and the private key. Encrypted private keys work too; enter the key
password in the Certificate Password field. If your certificate and
key are in separate PEM files, paste them into one file first.
Do I need an internet connection to sign?
Often, yes. The signing library fetches the issuer certificate chain
from the URLs in your certificate's Authority Information Access
extension, and if those servers can't be reached, signing fails for
certificates that need chain validation. Your PDF and private key
are never part of those requests; only the certificate URLs are
fetched.
Why does Adobe Reader say the signature validity is unknown?
The reader can't trace the certificate back to a root it trusts.
That's expected for self-signed certificates, which are fine for
testing but always show a warning. For documents other people need
to rely on, use a certificate issued by a Certificate Authority that
PDF readers trust.
Do I have to add a visible signature on the page?
No. The cryptographic signature is embedded whether or not the
visible block is enabled. Turn on Visible Signature if you want a
stamp on the page: pick the first, last, all, or a specific page,
set the position and size in points, and add a PNG, JPG, or WebP
image or a line of text; with neither, the tool writes the
certificate's common name and the current date.
What are the Reason, Location, and Contact Info fields for?
They're optional metadata stored inside the signature itself. Reason
records why you signed, such as "Approved" or "Reviewed", Location
where it happened, and Contact Info how to reach you. PDF readers
display them in the signature panel.
Can a digitally signed PDF still be edited?
The file can still be opened and edited, but any change made after
signing breaks the integrity check and readers will report the
document as modified. If the PDF has form fields or annotations that
should be fixed in place, run it through
Flatten PDF
before signing, not after.
How can I check that the signature was applied correctly?
Open the signed file in
Validate Signature. It lists every signature, shows the signer and issuer, checks the
certificate dates, and confirms whether the bytes have changed since
signing. You can also load your CA certificate there to verify the
trust chain.