PDFs are better since you can zoom pretty much infinitely, and print at a high quality. If you're making the font in Illustrator, and it's just outlines, anyone who wants to steal it will have to go through a lot of work to actually steal it—like copy the glyphs into a font editor, space it properly, fill in any needed (but missing from specimen) glyphs. Basically, the only people who not only want the font, but have the know-how to actually turn it into a font, will be the ones who wont just steal it, I think.

Anyway, a PDF probably isn't a big deal. If they reaally want the font, they'll probably ask you about it.

It’s a Open Type Font, drawn in Fontlab (and it has been a lot of work).
Pngs could be in 300dpi, too.

But probably you’re right. Most likely the ones that are able to steal the font are either professionals and wouldn’t do it or they are just bad designers ;-)

But aren’t printable pngs with the type in different sizes the better way to do it anyway?
This would avoid a illegal copy of the unfinished font, bad or not spaced at all.

In Illustrator, just convert your text to outlines if you're worried. (I think it's cmd+shift+o) Because outlines would be too much work to try and mess with.

PNGs are okay for quick previews, but on Typophile we really prefer PDFs for really looking at things. Like I said, converting to outlines should be enough protection if you're worried.

No, i’m not worried, rather looking for an alternative. The problem with converting to outlines is that it doesn’t look the same as real type. But this has been discussed before and I don’t want to resolve past issues… I think I’ll just use a pdf and don’t think about that stuff, I’m not sure if anybody is interested in my font at all. :)

Thank you very much for your attention!

No problem. Would like to see your typeface. :) (selfish motive revealed!)

The problem with converting to outlines is that it doesn’t look the same as real type

You will need to do it when you produce the PDF:
http://typophile.com/node/76217#comment-439419

Thank you for the links. Unfortunately it doesn’t help me in this case, but it’s very useful anyway!

I came back to the security settings, restricting everything but viewing and printing really should be enough. http://typophile.com/node/43834#comment-270258

Also, note that the "convert to outlines" problem is with InDesign's command, not Illustrator's. I have not had problems in Illustrator.

I know, you have to install the latest update, then it should work in InDesign as well.