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The Preview application in OS X Lion includes the ability to take a screen capture of your written signature and save it for later application in to any PDF file.

Where does Preview store the image file for this signature? Is it possible to extract the signature for use in another application like Adobe Reader?

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4 Answers 4

up vote 7 down vote accepted

You can alternatively try to insert your signature in a blank pdf document, crop to take only your signature and then save the document as a PNG file.

FYI, it's seems that the signature is stored in a .plist file. The file name is "com.apple.Preview.signatures.plist" and it's in folder : /Users/YourAccount/Library/Containers/com.apple.Preview/Data/Library/Preferences/

Hope this helps !

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Yes! That's definitely the image data. Now to decrypt it. Thanks! –  Ian C. Apr 23 '12 at 19:19
    
Awesome find! That is quite helpful! –  Daniel Lawson Apr 23 '12 at 19:40
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The decryption key is stored in the keychain. It's called Preview Signature Privacy. Currently I'm trying to figure out which algorithm they used to encrypt. –  Julian Jul 9 '13 at 13:15
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It appears that Preview stores the signature files in an undocumented, encrypted form directly in the Keychain. Without hacking their encryption and storage format, the file cannot be extracted...

but if you can make the signature appear on screen, you can capture a screen shot of said signature, and use that file in another application.

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The description on the keychain entry says it's a password to decrypt the files, not the image itself. It's possible there's a file on disk I can decrypt. I have the password in Keychain available to me. I'd just need to the know the file and the encryption type (and not even really that). –  Ian C. Apr 23 '12 at 18:18
    
Good call! I'll keep hunting for the file. –  Daniel Lawson Apr 23 '12 at 19:32
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this solution worked for me using 10.8.2 (mountain lion)

http://www.stuartcarnie.com/2011/08/transferring-preview-app-signatures-in.html

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  1. Insert your signature in preview on a blank part of a pdf page
  2. Press Shift+Command+4 to choose image for a screen shot
  3. Use the + that appears on screen to choose the signature for as your screen shot
  4. Open the screen shot and export as pdf, save

You now have a pdf of your signature that can be used, for example, in Adobe Acrobat.

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