Question

Situation:

• (Large) PDFs are stored on an iOS device
• The PDFs are encrypted using a Rijndahl algorithm
• When tapping one of the PDFs, it gets decrypted and afterwards viewed using a PDF viewer I implemented. The viewer is using the Core Graphics functionality to render the document page by page.

Issue:

• With the documents being large enough, encrytion will take a while.
• Viewing can only be started after the whole document has been decrypted into a temp file.

I’m wondering, if there is a way to…

• Pass some kind of stream to CGPDFDocument instead of a file URL
• Or any other alternative to be able to view as many pages as possible whil decrpytion is continued in the background?

Answer 1

If you cannot split your original PDF files down to single pages (as I suspect), then the following approach should work:

A: When still decrypting:

1. try to open the PDF document as you already do;

2. try accessing the document page you are interested in;

3. if it does not fail, render the page;

4. if it fails, then you know that page is not available yet (while decrypting);

5. while decrypting, release the pdf document each time you try to get a new page.

B: when decryption is done: do as you are already doing.

Please note that this is just a suggestion, I have not tried this while decrypting a document, but if point 1. does not fail, then this should work.