PDFViewerWhat are PDF passwords and permissions?
PDF passwords come in two kinds: an open (user) password that encrypts the file so nobody can read it without the key, and an owner (permissions) password that leaves the file readable but asks readers to block printing, copying or editing. The first is real security; the second is a request that any tool can ignore, which is why this viewer can remove restrictions but cannot open a locked file.
Open password vs owner password
The PDF specification defines one encryption system with two passwords:
| Open (user) password | Owner (permissions) password | |
|---|---|---|
| What happens when you open the file | A password prompt; nothing is shown until you enter it | The file opens normally |
| What it protects | The content: pages, text and images are encrypted | Nothing cryptographically; it sets permission flags |
| What a reader does | Must decrypt with the key derived from the password | Is asked to honor the flags (no print, no copy, no edit) |
| Can it be removed without the password | Only by guessing or brute force | Yes, by any tool that chooses not to honor the flags |
A file can have both. If it has only an owner password, the content is actually encrypted with an empty user password, which every reader applies automatically; that detail is the whole reason permission locks are weak.
What the owner password really protects
The owner password controls a set of permission bits stored in the file: print (none, low resolution, high resolution), copy text and graphics, modify, add or change annotations, fill form fields, extract for accessibility, and assemble (rotate, insert, delete pages). A reader that respects the standard greys out the matching buttons. Acrobat, Preview and Chrome all do.
But the content is readable by definition, since the file opens. Any software that can draw the page can also copy its text or print it; honoring the bits is a courtesy, not a technical barrier. Open-source tools such as qpdf, and many online unlockers, simply rewrite the file without the flags. So an owner password keeps honest users inside the lines (useful for a company template or an exam paper) but does not stop anyone determined. It also blocks you, the legitimate owner, when the person who set it has left the company; that is the most common reason people search for how to remove it.
Encryption strength: 40-bit, 128-bit, 256-bit AES
How hard an open password is to break depends on the algorithm, which depends on the producing software's age:
- 40-bit RC4 (PDF 1.1 to 1.3, 1990s): trivially broken in minutes on any computer regardless of password. Still produced by some old scanners and legacy systems.
- 128-bit RC4 (PDF 1.4): the algorithm is sound for its size, but the key derivation is fast, so short passwords fall to dictionary attacks.
- 128-bit AES (PDF 1.6): modern cipher, same fast key derivation.
- 256-bit AES (PDF 1.7 extension level 3 and PDF 2.0): current standard. With a long random password it is not practically breakable; with "password123" it still takes seconds.
In other words the password matters more than the bit count. A 12-character random passphrase on 128-bit AES beats a pet's name on 256-bit AES. For archiving note that PDF/A forbids any encryption at all.
What Remove Restrictions in this viewer does and does not do
Does: if a PDF opens without a prompt but printing, copying or editing is locked, Remove Restrictions strips the owner-password permission flags and writes a clean copy you can download. No upload: the file is rewritten by JavaScript in the tab. Use it for the unlock PDF tool or follow how to remove a password from a PDF.
Does not: open a PDF that asks for a password. The content is encrypted, there is no key in the file, and the viewer does not try to guess. It shows "This PDF is password-protected" and asks you to remove the password elsewhere first. If you know the password, open the file in Acrobat, Preview or Chrome, then print or save a copy without security; that unencrypted copy opens here normally. If you do not know it, recovery means a brute-force tool and a lot of time, with no guarantee.
Also outside scope: the viewer does not add passwords or permissions to a file. Adobe Acrobat, Preview (Export with a password), Microsoft Word (Save as PDF with Options), LibreOffice and qpdf all can.
Which protection to use for your own files
Use an open password with AES-256 and a long passphrase when the content is confidential: medical records, contracts, payroll. Send the password through a different channel than the file. Remember that once the recipient opens it, they can save an unprotected copy; encryption protects the file in transit and at rest, not against the reader.
Use permissions only when you want to signal "please do not edit" for a document that is not secret: a price list, a syllabus, a signed contract copy. It will keep casual readers from accidental changes and nothing more. For real tamper evidence, a digital signature certificate is the tool, which this viewer does not create (its signature feature places a drawn image, not a cryptographic signature).
Frequently asked questions
What is the difference between a user password and an owner password?
A user (open) password encrypts the content and must be entered to view the file. An owner password leaves the file viewable but sets permission flags that readers are asked to honor.
Can a PDF password be removed without the password?
Owner-only restrictions can be removed by any tool that ignores the permission flags, including this viewer. An open password cannot be removed without knowing or guessing it.
How secure is a password-protected PDF?
With AES-256 and a long random password, very secure. With old 40-bit RC4 encryption or a short dictionary password, it can be broken quickly.
Why can't I copy text from a PDF even though it opens?
The author set an owner password with copying disabled. The text is there; the reader is honoring the flag. Remove Restrictions in this viewer writes a copy without that flag.
Why does the viewer say this PDF is password-protected?
The file requires an open password and its content is encrypted. Open it where you can enter the password, save an unprotected copy, then load that copy.
Does an owner password stop someone from editing my PDF?
Only in readers that honor it. It is a request, not encryption, so anyone with an unlock tool can edit the file. For real protection use a digital signature or share a flattened copy.