is-pdf re-implementation

[dotemacs]

The idea is to remove the external dependency on org.apache.pdfbox/preflight.

The reason for that is since there is one less dependency, it's one less thing to worry about when the project needs dependency updates.

And the check this dependency performed is something light so why not have it on it's own.

[dotemacs]

I'll leave this here for a little while to see if anybody who watches this project, has any comments on it.

Thanks

[tirkarthi]

I think this can be closed since preflight is removed.

[dotemacs]

Maybe.

This really wasn't about Preflight, but more about checking if the file supplied is really a PDF file.

So I can leave it here as a reminder to get around to it at some point.

[dotemacs]

It's stale, I'll close it