You can limit access to a PDF by setting passwords and by restricting certain features, such as printing and editing. Passwords cannot be added to a document if it is already signed or certified. Two types of passwords are available:

Document open password

With a document open password (also known as a user password), users must type in the password you specify to open the PDF.

Permissions password

When you set only a permissions password (also known as a master password), recipients don’t need a password to open the document. However, they must type the permissions password to set or change the restricted features.

If the PDF is secured with both types of passwords, it can be opened with either password. However, only the permissions password allows the user to change the restricted features. Because of the added security, setting both types of passwords is often beneficial.

All Adobe products enforce the restrictions set by the permissions password. However, if third-party products do not support or respect these settings, document recipients are able to bypass some or all of the restrictions you set.

You can set the following options when you create a PDF or when you apply password protection to a PDF. Options vary depending on the Compatibility setting. Security options are not available for PDF/X standards or presets.

Compatibility

Sets the type of encryption for opening a password-protected document. The Acrobat 3 And Later option uses a low encryption level (40‑bit RC4), while the other options use a high encryption level (128‑bit RC4 or AES). Acrobat 6.0 And Later lets you enable metadata for searching. Acrobat 9.0 And Later encrypts the document using the AES encryption algorithm with a 256-bit key size.

People using an earlier version of Acrobat cannot open a PDF document with a higher compatibility setting. For example, if you select the Acrobat 9 And Later option, the document cannot be opened in Acrobat 8.0 or earlier.

Encrypt All Document Contents

Select this option to encrypt the document and the document metadata. If this option is selected, search engines cannot access the document metadata.

Encrypt All Document Contents Except Metadata

Select this option to encrypt the contents of a document but still allow search engines access to the document metadata. This option is available when you select a compatibility to Acrobat 6.0 and later.

Encrypt Only File Attachments

Select this option to require a password for opening file attachments. However, users can open the PDF without a password. Use this setting for security envelopes. This option is available when you set compatibility for Acrobat 7.0 and later.

Require A Password To Open The Document

Select this option to require users to type the password you specify to open the document. This option is unavailable if Encrypt Only File Attachments is selected.

Document Open Password

Specify the password that users must type to open the PDF file.

Note: If you forget a password, there is no way to recover it from the document. It’s a good idea to store passwords in a separate secure location in case you forget them.

Restrict Editing And Printing Of The Document

Restricts access to the PDF file’s security settings. If the file is opened in Acrobat, the user can view the file but must enter the specified Permissions password to change the security and permissions settings. If the file is opened in Illustrator®, Photoshop®, or InDesign®, the user must enter the Permissions password. It is not possible to open the file in a view‑only mode.

Change Permissions Password

Specify a password that is required to change the permissions settings. This option is available only if the previous option is selected.

Printing Allowed

Specifies the level of printing that users are allowed for the PDF document.

None

Prevents users from printing the document.

Low Resolution (150 dpi)

Lets users print at no higher than 150‑dpi resolution. Printing can be slower because each page is printed as a bitmap image. This option is available only if the Compatibility option is set to Acrobat 5.0 Or Later.

High Resolution

Lets users print at any resolution, directing high-quality vector output to PostScript® and other printers that support advanced high-quality printing features.

Changes Allowed

Defines which editing actions are allowed in the PDF document.

None

Prevents users from changing the document that are listed in the Changes Allowed menu, such as filling in form fields and adding comments.

Inserting, Deleting, And Rotating Pages

Lets users insert, delete, and rotate pages, and create bookmarks and thumbnails. This option is only available for high (128‑bit RC4 or AES) encryption.

Filling In Form Fields And Signing Existing Signature Fields

Lets users fill in forms and add digital signatures. This option doesn’t allow them to add comments or create form fields. This option is only available for high (128‑bit RC4 or AES) encryption.

Commenting, Filling In Form Fields, And Signing Existing Signature Fields

Lets users add comments and digital signatures, and fill in forms. This option doesn’t allow users to move page objects or create form fields.

Any Except Extracting Pages

Lets users edit the document, create and fill in form fields, and add comments and digital signatures.

Enable Copying Of Text, Images, And Other Content

Lets users select and copy the contents of a PDF.

Enable Text Access For Screen Reader Devices For The Visually Impaired

Lets visually impaired users read the document with screen readers, but doesn’t allow users to copy or extract the contents. This option is available only for high (128‑bit RC4 or AES) encryption.

You can remove security from an open PDF if you have the permissions to do so. If the PDF is secured with a server-based security policy, only the policy author or a server administrator can change it.