Blog
Product news, and articles on digital signatures and certificates written to be understood. No newsletter, no comments, no tracking: there is an RSS feed if you want to follow along.
-
How to sign a PDF with a digital certificate on a Mac
From a certificate file to a signed PDF: what a signing certificate is, how it gets into the macOS keychain, how to sign with Adobe Acrobat and with PDFsigna, and how to check the signature afterwards.
-
Preview can’t sign with a certificate — and it breaks signatures
Preview only places a picture of your signature. Worse, saving a digitally signed PDF from Preview rewrites the file and the signature stops being valid. We measured it on macOS 27: what happens, how to tell, and how to avoid it.
-
Acrobat alternatives you buy once
Adobe no longer sells a perpetual Acrobat. What it sells instead, which PDF editors still have a one-time price, the four questions to ask before you pay — with every figure checked on the vendor’s own site in October 2026.
-
A visual signature is not a digital signature
Your handwriting placed on a PDF is not an advanced electronic signature. What each one is, what it is worth, and how PDFsigna tells you before you sign.
-
PDFsigna is on the Microsoft Store, and coming to the Mac App Store
Where to get PDFsigna, why only there, what it costs, and what isn’t ready yet.
-
How to check whether a PDF signature is valid
Three free ways to validate the signature on a PDF someone sent you — the European Commission’s DSS demo, Spain’s VALIDe and Adobe Acrobat — and what valid, indeterminate, invalid and modified actually mean.
-
B-B, B-T, B-LT, B-LTA: which PAdES level do you need?
The four levels of a PAdES signature in plain language: what each one adds, and when it is enough for an agreement, an invoice, or a document someone must still be able to verify in ten years.
-
Which certificate do you need to sign, and how to get one
Qualified or not, software or smart card: what a signing certificate is, the Spanish options (FNMT, ACCV, the national ID card) explained for everyone, and which ones PDFsigna can use today.
-
Why your signature needs a third party’s clock
What a timestamping authority is, why your own computer’s clock proves nothing, and why PDFsigna timestamps signatures with a qualified, free-for-personal-use authority.