PDF can encode various restrictions on document operations which can be granted or denied individually (some settings depend on others, though):

Printing: If printing is not allowed, the print button in Acrobat will be disabled. Acrobat supports a distinction between high-resolution and low-resolution printing. Low-resolution printing generates a bitmapped image of the page which is suitable only for personal use, but prevents high-quality reproduction and re-distilling. Note that bitmap printing not only results in low output quality, but will also considerably slow down the printing process.

General Editing: If this is disabled, any document modification is prohibited. Content extraction and printing are allowed.

Content Copying and Extraction: If this is disabled, selecting document contents and copying it to the clipboard for repurposing the contents is prohibited. The accessibility interface also is disabled. If you need to search such documents with Acrobat you must select the Certified Plugins Only preference in Acrobat.

Authoring Comments and Form Fields: If this is disabled, adding, modifying, or deleting comments and form fields is prohibited. Form field filling is allowed.

Form Field Fill-in or Signing: If this is enabled, users can sign and fill in forms, but not create form fields.

Content Accessibility Enabled: Allow accessibility software (such as a screenreader) to use the document contents. This setting is declared as deprecated in PDF 2.0; content extraction for accessibility purposes is based on the Content Copying and Extraction setting.

Document Assembly: If this is disabled, inserting, deleting or rotating pages, or creating bookmarks and thumbnails is prohibited.

Specifying access restrictions for a document, such as printing prohibited will disable the respective function in Acrobat. However, this not necessarily holds true for third-party PDF viewers or other software. It is up to the developer of PDF tools whether or not access permissions will be honored. Indeed, several PDF tools are known to ignore permission settings altogether; commercially available PDF cracking tools can be used to disable all access restrictions. This has nothing to do with cracking the encryption; there is simply no way that a PDF file can make sure it won’t be printed while it still remains viewable. This is described as follows in ISO 32000-1:

»Once the document has been opened and decrypted successfully, a conforming reader technically has access to the entire contents of the document. There is nothing inherent in PDF encryption that enforces the document permissions specified in the encryption dictionary.«

By default, PDF encryption always covers all components of a document. However, there are use cases where it is desirable to encrypt only some components of the document, but not others:

PDF 1.5 (Acrobat 6) introduced a feature called plaintext metadata. With this feature encrypted documents can contain unencrypted document XMP metadata. This is for the benefit of search engines which can retrieve document metadata even from encrypted documents.

Since PDF 1.6 (Acrobat 7) file attachments can be encrypted even in otherwise unprotected documents. This way an unprotected document can be used as a container for confidential attachments.