Where Base64 PDFs come from
APIs that return documents in JSON — invoicing, e-signature, shipping-label and reporting services — usually put the PDF in a string field as Base64, because JSON cannot carry raw binary. Email attachments are Base64 too (MIME wraps them at 76 characters per line). Paste any of these here: line breaks, a surrounding pair of JSON quotes and the data:application/pdf;base64, prefix are all handled.
The decoder checks the result really is a PDF by its signature: every PDF starts with the bytes %PDF-, which in Base64 is always JVBER. If your string starts differently, it is not a PDF, or something (such as a byte-order mark or a log prefix) was added in front.
Preview and download
The decoded bytes are turned into a local file object in your browser and shown with the built-in PDF viewer, so you can check it is the right document before saving it. The page count, PDF version and title are read from the file itself, and password-protected PDFs are flagged. Some mobile browsers do not display PDFs inline; use Download or Open in new tab instead.
Frequently asked questions
How do I convert Base64 to PDF?
Paste the Base64 string into the box. The PDF is decoded and previewed instantly; click Download PDF to save it. You can include or omit the data:application/pdf;base64, prefix.
Why does my Base64 start with JVBERi0?
That is "%PDF-" encoded in Base64 — the header every PDF begins with. If you see JVBERi0, the string is a PDF.
Why do I get "not a PDF"?
The Base64 decoded fine but the bytes are another format — the message tells you which when it can recognise it (for example PNG or ZIP). Check that you copied the right field, and the whole value.
How do I decode Base64 to PDF on the command line?
On Linux or macOS: base64 -d input.txt > output.pdf (older macOS: base64 -D). In PowerShell: [IO.File]::WriteAllBytes("out.pdf", [Convert]::FromBase64String((Get-Content input.txt -Raw))).
Is the PDF uploaded?
No. Decoding and preview happen entirely in your browser; the document never leaves your device. That matters for invoices, contracts and IDs.