About PDF encryption checker
A narrow tool on purpose. It reads the encryption dictionary at the top of the PDF — the small structure that declares which security handler, cipher and revision the file uses — and tells you what it found. Nothing else. You learn whether the document is encrypted, which algorithm protects it (AES-256, AES-128, or an RC4 variant), which encryption revision number it declares, whether opening the file demands a user password, and the key length in bits. Because this information lives in the clear rather than inside the encrypted portion, the check works on files you cannot open: no password is requested and none is needed. Triage is therefore its natural use — confirming that a batch you just encrypted really did come out as AES-256, or identifying a file that is still protected by weak legacy RC4 and needs re-encrypting before it goes into an archive.
How to PDF encryption checker
- 01
Load any PDF
Encrypted or not, and locked or not. The encryption dictionary is readable without the password.
- 02
Read the verdict
The report leads with a plain yes or no, then names the cipher, revision and key length.
- 03
Act on weak results
If it reports RC4 or an old revision, re-encrypt the file with Encrypt PDF once you can open it.
What this tool does
- Works without the password — the encryption dictionary is not itself encrypted
- Names the exact cipher and PDF encryption revision, not a vague strength rating
- Flags RC4 and 40-bit key lengths as legacy and weak
- States whether an open password is required, separately from the cipher
- Report only — the document is never modified or re-saved
Limitations worth knowing
Every PDF tool has constraints. Stating them plainly is more useful than discovering them halfway through your work.
- Reports what the file declares. A tool that wrote an incorrect encryption dictionary would be reported as it describes itself.
- Does not evaluate password strength — a strong cipher with a three-character password still reports as AES-256.
- Says nothing about permission flags; use PDF Permissions Checker for those.
- Certificate-based encryption is identified as such but its certificate details are not enumerated.
How your file is handled
This tool runs entirely inside this browser tab. When you choose a file, your browser reads it from your own disk and hands the bytes to JavaScript running on this page — no network request carries your document anywhere. You can confirm that yourself: open your browser’s developer tools, switch to the Network panel, and run the tool. You will see no upload.
Nothing is stored after the fact. Closing or reloading this tab discards the file, the result and everything derived from them, because none of it ever left your machine. Read how local processing works.
Questions about PDF encryption checker
Can it check a PDF I cannot open?
Yes, and that is the main use. The encryption dictionary sits in the readable structure of the file, so the cipher and revision can be reported without the password.
It says AES-256. Does that mean the file is safe?
It means the algorithm is current. Safety also depends on the password the key was derived from, which no inspection can measure. A strong cipher with a guessable password is a weak file.
What should I do if it reports RC4?
Treat that file as effectively unprotected — RC4 is an obsolete cipher whose weaknesses are well documented. Decrypt it using the password you hold, then re-encrypt with AES-256.
Why does it report encryption on a file that opens without a prompt?
Because the file most likely has an owner password only. It is genuinely encrypted, but with an empty user password, so any reader opens it while the permission flags claim restrictions.
Tools that pair with this one
- PDF Permissions CheckerRead the permission bits a PDF sets — and what they are really worth.
- PDF Security InspectorEvery security-relevant feature of a document, inventoried in one pass.
- PDF Version CheckerCheck which PDF version a file claims, and what that version can and cannot do.
- PDF Security AnalyzerNot just what is in the file — which parts of it are a problem.
- PDF Metadata ViewerRead the fields a PDF carries about itself, including the raw XMP.
- PDF Metadata RemoverClear selected document properties before sharing; this is not secure anonymisation.