Add static factory for existing files

[Schrank]

Fixes #56

[horstoeko]

Hi @Schrank,

Thank you for your PR. As I am always picky, I would like you to rename the variable $pdfData in the method signature to something more catchy. You assume that it must be a file name (your method is called "fromPdfFile". So I would think that the variable would be better named $pdfFileName. Furthermore, it would only be logical if you also had a fromPdfString method. Would you be so kind as to implement this accordingly? Otherwise I can only say: Good idea!

Best regards...

[Schrank]

Done. I would love to add tests, but don't have the motivation to setup the project locally.

Therefore: It is untested (sorry, should have mentioned that!)

[horstoeko]

Done. I would love to add tests, but don't have the motivation to setup the project locally.

I think this is no problem in this case

Therefore: It is untested (sorry, should have mentioned that!)

Noted... Merging...

Best regards