Hi Barry, well certian kinds of shapes just tend to be difficult to fillet in general - does your PDF have stuff like very sharp corners in it or maybe some little tiny segments that are not quite smooth to each other, or also possibly things like little curly-cues in it where the path criss-crosses back over itself? Those are a few of the kinds of things that can then make it difficult to do fillets in general.

So it's not that it's inherent to PDF, it totally depends on the particular shape of the particular stuff in your PDF file. If you were to post the PDF file here or e-mail it to me at moi@moi3d.com if you want to keep it private, that would help a lot to give you some more specific advice - it's hard to give you any specific information without actually seeing the thing you are trying to fillet.

Fillet though can be pretty sensitive to a lot of things, it has to do a lot of difficult calculations like generate offset surfaces, intersect those offset surfaces, make fillet surfaces that follow those intersection curves, extend fillet surfaces so they run into each other and trim them with each other and build corner patches where multiple fillets come to a single point. Each of these things is a difficult calculation and can be especially hard with certain kinds of shapes or arrangements of curves.

Another thing that can make it difficult is if your fillet radius is larger than the bends in the curves - that causes the fillet to bunch up on itself. You mention just trying 0.5 and 1.0 values, if you have tight bends in your shape you may need to use lower radius values than that.

- Michael