Support

What do I need to sign a PDF with a Japanese My Number Card?

Three things. Signing is done from the menu: Tools → "Digital Signature (Certificate)..." — this is the certificate-based signature, not the handwritten-look "Signature" annotation.

• A My Number Card that carries a signing certificate (署名用電子証明書)
• An IC card reader. A supported Android phone can stand in for one: install the JPKI app on the phone as well, pair it to the Windows PC over Bluetooth, then leave the phone on "PC connection" → "Start PC connection". An iPhone cannot be used this way. NFC alone is not enough — check the JPKI list of supported handsets
• The JPKI client software (公的個人認証サービス 利用者クライアントソフト). With an IC card reader, installing it is enough — you never need to launch it to sign. Only the phone-as-reader route uses its window, to turn on the setting that lets a smartphone act as the reader

The JPKI client comes in 64-bit and 32-bit builds. If the wrong one is installed, the signing dialog says so in its "JPKI Middleware:" field; reinstall the matching build.

Step-by-step instructions ship with the app: Help → "Digital Signing Guide (My Number Card / .pfx)".

Is the signing password the card's 4-digit PIN?

No. Signing uses the password of the signing certificate: 6–16 alphanumeric characters, letters in uppercase, set at your municipal office. The 4-digit PIN is a different credential.

If you enter the 4-digit PIN, the app stops it before it reaches the card, so mixing them up cannot burn an attempt.

What happens if I get the password wrong?

The signing certificate locks after five consecutive wrong entries. Clearing it means resetting the password — either through the JPKI smartphone app together with a convenience-store kiosk terminal, or at the municipal office that issued the card. Either way it is a trip, so we suggest stopping to check after two failures.

When the screen says the password was not sent to the card, no attempt was consumed. The "Check the card (no password needed)" button in the signing dialog never sends a password, so you can press it as often as you like.

Signing fails. What should I check?

Press "Check the card (no password needed)" under the card section of the signing dialog. It walks through each stage of reading the card and reports where it stopped. The button never sends a password to the card.

• Stops at the JPKI client check — the JPKI client is not installed, or its 64/32-bit build does not match
• Stops at loading or preparing the signing module — restart Windows; if it persists, reinstall the JPKI client
• Stops at the card reader check — no reader was found. If you are using a smartphone instead, confirm the Bluetooth pairing and that the phone is sitting on "PC connection" → "Start PC connection"
• Stops at checking or connecting to the card — reseat the card. With a smartphone, hold the card still against the NFC area

Seeing "not attempted on purpose" at the certificate-read stage is normal. The signing certificate contains your name and address, so the card itself keeps it behind the password; it is read at the moment you actually sign.

When a smartphone is standing in for a reader, the "Card Reader:" field staying "unknown" is normal — there is no physical reader to detect, so that field cannot tell you anything.

Can I sign with a .cer file?

No. A .cer holds only the public certificate, with no private key, so it fails with an error saying the selected certificate has no usable private key. File-based signing needs .pfx or .p12.

A My Number Card's private key cannot leave the card by design, so you cannot export a .pfx from it. To sign with the card, leave the card option selected instead of picking a file.

Can I sign with a non-Japanese eID card (eIDAS and similar)?

Card-based signing goes through the JPKI client only, so eIDAS-style smart cards are not supported. If your issuer supplies a certificate file (.pfx / .p12), file-based signing may work, but we have not verified it and cannot guarantee it.

I cannot open a password-protected PDF.

Check these in order.

• Only single-byte alphanumeric passwords are supported. If the IME is in full-width or hiragana mode the characters will not match even though they look the same — switch to single-byte input
• A PDF can carry a user password (needed to open the file) and an owner password (which restricts editing). Opening the file requires the user password
• Some AES-256 encrypted files cannot be opened, a limitation of the underlying library

Do I need to install .NET or any other runtime?

No. Everything is bundled in the installer and no separate install is required.