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How to decrypt a PDF file

Decrypting a PDF means using the password to turn the encrypted file back into a readable one and saving the result. It does not mean breaking the encryption, which is a different thing and is not possible. The word gets used for both, which is why people search for it expecting more than it delivers.

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The word means two things

In normal use, decrypting a PDF is what happens every time somebody types the right password: the viewer turns the scrambled content back into pages. Saving that result as an unencrypted file is what people mean when they ask how to decrypt one permanently.

The other meaning, getting into a file without the password, is the one search results promise and nothing delivers. Keeping the two apart saves a lot of wasted time, because the first is a one step job and the second is not a job at all.

What PDF encryption actually is

An encrypted PDF stores its page content, and often its embedded fonts and images, as ciphertext. A password produces the key that decrypts them. Nothing about the pages is readable without it, which is why a protected file cannot even report its page count.

When this site applies protection, it uses AES with a 128-bit key and sets the file version to one that supports it. Files from other software may use an older or a stronger scheme, and the unlock tool reads whatever is there rather than assuming.

Decrypting with the password

Open the unlock tool, choose the file, type the password and download. The result is a genuinely unencrypted PDF: the tool reopens the finished file without supplying any password and checks that it is no longer encrypted before it offers the download.

That check is the difference between decrypting a file and hiding the dialog. A copy that still carried encryption with a blank password would look decrypted to you and behave like a protected file everywhere else.

The permissions-only case

Some encrypted PDFs open with an empty password and only exist to record restrictions. They are encrypted in the technical sense, so other tools still refuse them, but there is nothing for you to type.

The unlock tool detects that state and produces a decrypted copy with no password step at all. The editing guide covers what those restrictions are trying to do and how much weight they carry.

What comes out

A complete document. Pages are copied whole, so text stays selectable, images keep their pixels and page sizes are unchanged. The document properties are carried across as well, which means the decrypted copy still names its author, producer and dates.

Nothing is re-rendered or recompressed. Decryption is not a conversion, and the file you get differs from the original only in that it is no longer locked.

Encrypting it again

The reverse operation sets a new password on the protect page. One password serves as both the open password and the owner password, and every permission is granted, so the file is either open to whoever has the password or closed to everyone else.

A PDF that follows the PDF/A archival standard is refused rather than encrypted, because adding encryption would break the format it was made to satisfy. The unlocking guide covers working out which state a file is in.

Why other tools refuse an encrypted file

Merging, page organising, compression and image export all need to read the pages. An encrypted file gives them ciphertext, so they stop rather than produce something broken. That is true of the permissions-only kind as well, even though it opens perfectly well in a viewer.

So decrypting is usually not the job you came for, it is the step before the job. Save the decrypted copy once and every other tool on the site accepts it, including the ones that had been refusing the file with an error you could not act on.

Questions people ask

Is decrypting a PDF the same as cracking its password?
No. Decrypting means using the password to produce an unencrypted copy, which takes one step. Getting into a file without the password is not a step that exists, because the content is real ciphertext.
What encryption does this site use when protecting a file?
AES with a 128-bit key, with the file version set to one that supports it. Files made elsewhere may use a different scheme, and the unlock tool reads whichever is present.
How do I know the copy is really decrypted?
The tool reopens the finished file without giving it any password and checks that it reports as unencrypted. If that check fails, nothing is offered for download.
Does decryption change how the pages look?
No. Nothing is re-rendered or recompressed. The decrypted file differs from the original only in that the content is no longer scrambled.
Does the decrypted copy change size?
Only a little. Encryption scrambles the stored streams, it does not compress them, so taking it off leaves the same page content at close to the same byte count. A file that was too large to email before is still too large afterwards.

Do it now

The tool runs in this browser. Your file never leaves the machine, and the result is checked before you download it.

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