The issue here is largely caused by Apple's change to the Document model introduced in Lion, with changes to the document being auto-saved. While this behaviour is desirable in, say, a Word processor, it's not so desirable in an app like Preview, which is often used for Viewing originals that should not be edited.

You can turn off Apple's Auto-save in Preview with the following Terminal command:

defaults write -app 'Preview' ApplePersistence -bool no

As a result, if you accidentally click on the document and create a Text Annotation, the change will not be saved unless you manually save the document.

EDIT: This no longer seems to work in Mojave and upwards. If you truly want a read-only PDF viewer, you may need to use another application.

The issue here is largely caused by Apple's change to the Document model introduced in Lion, with changes to the document being auto-saved. While this behaviour is desirable in, say, a Word processor, it's not so desirable in an app like Preview, which is often used for Viewing originals that should not be edited.

You can turn off Apple's Auto-save in Preview with the following Terminal command:

defaults write -app 'Preview' ApplePersistence -bool no

As a result, if you accidentally click on the document and create a Text Annotation, the change will not be saved unless you manually save the document.

EDIT: This no longer seems to work in Mojave and upwards. If you truly want a read-only PDF viewer (or one that requires explicit saves), you may need to use another application.

The issue here is largely caused by Apple's change to the Document model introduced in Lion, with changes to the document being auto-saved. While this behaviour is desirable in, say, a Word processor, it's not so desirable in an app like Preview, which is often used for Viewing originals that should not be edited.

You can turn off Apple's Auto-save in Preview with the following Terminal command:

defaults write -app 'Preview' ApplePersistence -bool no

As a result, if you accidentally click on the document and create a Text Annotation, the change will not be saved unless you manually save the document.

The issue here is largely caused by Apple's change to the Document model introduced in Lion, with changes to the document being auto-saved. While this behaviour is desirable in, say, a Word processor, it's not so desirable in an app like Preview, which is often used for Viewing originals that should not be edited.

You can turn off Apple's Auto-save in Preview with the following Terminal command:

defaults write -app 'Preview' ApplePersistence -bool no

As a result, if you accidentally click on the document and create a Text Annotation, the change will not be saved unless you manually save the document.

EDIT: This no longer seems to work in Mojave and upwards. If you truly want a read-only PDF viewer, you may need to use another application.