How to use a .pfx digital certificate on your Android phone

A software digital certificate is a file, usually with a .pfx or .p12 extension, protected by a password. Because it is just a file, you can use it on your phone to sign PDFs.

This guide shows how to copy the certificate to Android, when it is worth installing it in the system and how to sign with Pdf Tools, without uploading the certificate to any website.

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Certificate file or token: which one do you have?

Some certificates are issued as a file (.pfx or .p12) that you keep on your computer; in some countries this type is called an A1 certificate. Others are stored on a USB token or a smart card and cannot be copied. To use a certificate on your phone with Pdf Tools, it must be a software certificate in a .pfx or .p12 file. Tokens and smart cards are not supported.

How to copy the .pfx file to your phone

Find the certificate file on your computer (.pfx or .p12 extension). If it is only installed in your computer's certificate store, the issuer or your IT team can help you export a password-protected copy that includes the private key.
Copy the file to your phone by USB cable, which is the safest option, or through your personal cloud storage.
Keep the certificate password at hand. You will need it when signing.
After copying, delete the file from any shared folders or chats you used.

Do you need to install it on Android?

No. Pdf Tools can use the .pfx file directly: just pick the file and enter the password when signing.

If you prefer to install it, search for "Install certificate" in Android Settings (the path varies by brand, but it is usually under Security or Encryption & credentials) and choose to install a user certificate. Android requires a screen lock to install certificates. Pdf Tools then shows the installed certificate in its list.

How to sign the PDF

Open Pdf Tools and tap Sign with A1 Certificate (PFX).
Pick the PDF.
Choose the .pfx file or the installed certificate and enter the password.
Save. The signed PDF gets a stamp with the holder's name and the date and goes to the Signed folder in My Files.

Security tips

Never send the .pfx file and its password together to anyone.
Do not upload your certificate to websites that offer to sign for you.
Keep a screen lock on your phone.
If you lose your phone, contact the certificate authority to revoke the certificate.

Good to know

Pdf Tools signs with CMS/PKCS#7 and SHA-256, without a timestamp, and does not follow the PAdES standard. If the recipient requires PAdES or a qualified electronic signature, check first that they accept this type.

Frequently asked questions

Can I use the same certificate I use on my computer?

Yes, if it is a software certificate in a .pfx or .p12 file. It is the same file.

Does it work with a token or smart card?

No. Tokens and smart cards are not supported by Pdf Tools on the phone.

Is my certificate sent to a server?

No. The file and its password are used only on the device, at the moment of signing.

I forgot the certificate password. Can the app help?

No. The password is set when the certificate is issued or exported. Contact the issuer.