Working with PDFs on mobile is a pain. On the bright side at least Apple provides us CGPDFDocument
However examples on how to use CGPDFDocument are limited to the bare basics. On a recent project, I though I had a pretty basic requirement. Provide the user with the ability to remove the password for a protected PDF file. How hard could this be? Unfortunately I wasn’t able to find any examples on how to do this so decided to put my own together.
The most important thing you need to know about working with CGPDFDocument is it is immutable. This means you can’t just call unlockWithPassword and update a property to remove the password.
This means you will need to first unlock the PDF, then create an entirely new document. If you are working with large files you will need to be careful about the memory you are using. Instruments will be your best friend.
Let’s walk through an example. First we need to load a PDF file into a Data object as shown below.
Next you need to unlock your PDF using the existing password. In the example below we create a helper function called unlock that takes the Data from our PDF file and returns an unlocked CGPDFDocument. If the method is unable to either cast the Data object or unlock using the provided password a nil is returned.
We now have an unlocked CGPDFDocument object. Since this is immutable we need to use this as the source to create a new CGPDFDocument without a password. This is done by looping through the now unlocked CGPDFDocument and copying each CGPDFPage into a new CGPDFDocument. The copyPDFtoData helper function in the below example shows how the Core Graphics context is managed as part of the looping process. The end result is a Data object that is a copy of the PDF we started with, but without the password.
Keep in mind this isn’t an exact copy. The CGPDFDocument info and other meta data won’t be copied as part of this process. This can easily be added to the copyPDFtoData but was overkill for this example.
For convenience I’ve combined the above helper functions into a single class for easy maintenance and experimentation.
For more comprehensive PDF handling check out my PDFUtilities project.