Fix for split-pdf

[dotemacs]

Description of your pull request

Previously with-open was used to open the PDF document that would be split. Which is fine if you're just thinking about closing the file after you've split it. But it doesn't seem very useful, because once you've split the file, you probably want to do something with it.

I'm reverting this change introduced via
2ed5824 just to get some opinions in this issue: #46

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