If you are looking for a serious answer to a legal question, there is no other way than to ask an attorney in your country, because the meaning of a license like LPPL depends on the legal frames of the countries around the world.
Given, that we do not know your country and a lot of other details, on which a serious answer depends, I guess that any PDF you generate using software under the LPPL, is not a »derived work«, except a PDF which contains the software or parts of it.
In reply to Frank Mittelbach's answer above and comment below: One could argue, that the sentence »running the Work...« says nothing about the output produced by »running the WORK«. If one is allowed to run a software it may not be included that one is free to use the result.
It would be more clear, if clause 1 of the conditions of the LPPL stated that the results produced neither are derived works nor in the scope of the licence.
From my (German) way of interpreting this licence it seems not impossible to construct an argument that the result of the software were derived work, although running the software is free. A special case is a PDF containing the text of the WORK.
I would not follow this argument, but if our OP resides in the USA, we have to concede that a lawsuite SCO ./. rest of the world (e.g. see here) was possible there. We can not exclude it for all countries of the world.