Base64 to PDF & File Converter · PDF to Base64

Base64 to PDF — quick answers

What is a Base64 PDF?

%PDF-1.4          → bytes 25 50 44 46 2D 31 2E 34
JVBERi0xLjQ=      → the same bytes in Base64
data:application/pdf;base64,JVBERi0xLjQ=   → data URI form

Features

Base64 to PDF in Python, Java, JavaScript and more

Base64 to PDF examples

JVBERi0xLjQKMSAwIG9iago8PCAvVHlwZSAvQ2F0YWxvZyAvUGFnZXMgMiAwIFIgPj4K…

PDF · version 1.4 · downloaded as file.pdf

"data:application\/pdf;base64,JVBERi0xLjQK…"

Read as: removed the surrounding quotes → undid JSON escapes → removed the data URI prefix (application/pdf)

{"code":0,"data":{"name":"invoice.pdf","file":"JVBERi0xLjQK…"}}

Read as: took the field data.file out of the JSON

data:application/pdf;base64,iVBORw0KGgoAAAANSUhEUgAA…

Warning: the data URI says application/pdf, but the bytes are PNG. Saved as file.png

255044462d312e370a…

Warning: this looks like hexadecimal — read as hex it is a PDF. [Decode as hex]

How to convert Base64 to PDF

1. 1

   Paste the Base64 as you got it

   Raw Base64, data:application/pdf;base64,…, a string copied out of JSON with \/ escapes, or the whole API response. For very long strings use Open a .txt file instead of pasting.

2. 2

   Check how it was read

   The line under the box lists every clean-up step — prefix removed, escapes undone, padding added, field taken from the JSON. If something is wrong, the error names the exact character and position.

3. 3

   Look at the detected type and warnings

   The badge shows the type read from the file's magic bytes. A yellow note appears if it is not actually a PDF, if the data URI lies about its type, or if the PDF is cut off before %%EOF.

4. 4

   Preview and download

   PDFs open in the browser's own viewer, images and text are shown inline. Rename the file if you like and click Download. For the reverse direction, switch to PDF / file → Base64 and drop a file.

Why a Base64 PDF will not open: common mistakes

base64.b64decode(value)  # value = 'data:application/pdf;base64,JVBERi0…'

b64 = value.split(',', 1)[1] if value.startswith('data:') else value
pdf = base64.b64decode(b64)

fs.writeFileSync('out.pdf', Buffer.from(b64, 'base64').toString())

fs.writeFileSync('out.pdf', Buffer.from(b64, 'base64'))

byte[] pdf = Base64.getDecoder().decode(wrapped);  // IllegalArgumentException

byte[] pdf = Base64.getMimeDecoder().decode(wrapped);

base64.b64decode(token_part)  # contains - and _

base64.urlsafe_b64decode(token_part + '=' * (-len(token_part) % 4))

new Blob([atob(b64)], { type: 'application/pdf' })

const bytes = Uint8Array.from(atob(b64), c => c.charCodeAt(0));
new Blob([bytes], { type: 'application/pdf' })

SELECT LENGTH(pdf_b64) FROM docs;  -- 65535: suspiciously round

ALTER TABLE docs MODIFY pdf_b64 LONGTEXT;  -- or store the bytes in a BLOB

When you need Base64 to PDF

An API returns the PDF as Base64

Invoicing, e-signature and label-printing APIs often return documents inside JSON. Paste the response to check the document before writing the code that saves it.

Debugging a PDF that will not open

When the saved file is blank or corrupt, paste the same Base64 here. The tool tells you whether it is truncated, double-encoded, not a PDF at all, or fine — which means the bug is in how your code writes the file.

Sending a file in a JSON request

Many upload endpoints expect {"filename": …, "content": "<base64>"}. Encode the file here to build a test request for Postman or cURL.

Embedding a file in HTML, CSS or email

Produce a data URI for an inline PDF link, a font or a small image, or 76-column Base64 for a MIME email part.

Reading attachments from logs and databases

Files stored in a text column or printed to a log can be pulled straight back out — and a missing %%EOF tells you the column or the log line was too short.

How Base64 file encoding works

Why Base64 is 33% bigger

Each character carries 6 bits, so 3 bytes (24 bits) need 4 characters. The length is 4 × ⌈n ÷ 3⌉ with padding: 100 KB (102,400 bytes) becomes 136,536 characters. MIME wrapping adds CRLF after every 76 characters, so 1 MB becomes 1,434,896 instead of 1,398,104.

Standard and URL-safe alphabets

RFC 4648 defines two alphabets that differ only in the last two characters: + / (standard, section 4) and - _ (URL- and filename-safe, section 5). URL-safe Base64 usually omits = padding. Mixing both in one string means it was edited or joined.

Padding and impossible lengths

Padding = makes the length a multiple of 4. Without it, a remainder of 2 or 3 can be restored; a remainder of 1 is impossible for any valid Base64 — a character was lost or added. = in the middle usually means two strings were concatenated.

Magic bytes decide the type

A file declares its format in its first bytes: %PDF- for PDF, 89 50 4E 47 for PNG, 50 4B 03 04 for ZIP-based formats such as DOCX and XLSX. Those bytes fix the first Base64 characters, so the type can be read before decoding — see the table in the tool.

How a truncated PDF is detected

A PDF ends with %%EOF. If it does not appear in the last 1,024 bytes, the file was almost certainly cut short. The header may start up to 1,024 bytes in; most readers still open such files, so it is reported but not rejected.

Best practices for sending files as Base64

Send the MIME type and the file name with the data

Base64 carries no name or type. Put both next to it ({"filename": "invoice.pdf", "mime": "application/pdf", "content": "…"}) or use a data URI, so the receiver does not have to guess.

Check the magic bytes on the receiving side

Before saving, verify that the decoded bytes start with %PDF-. It catches wrong fields, double encoding and error pages returned as Base64 in one line of code.

Prefer multipart or a URL for large files

Base64 adds a third to the size and the whole string has to sit in memory. Above a few megabytes, multipart/form-data or a pre-signed download URL is lighter for both ends.

Store bytes, not Base64, in the database

A BLOB/bytea column is a third smaller and cannot be silently truncated like a VARCHAR. Encode to Base64 only at the API boundary.

Base64 to PDF — FAQ