One would hope that - with the advent of ISO 32000 - PDF documents would all be of same quality. Alas - this is not the case.
The Basics - How are PDF Files Created
There are two basic steps in the process. The first is to use your PDF application which creates a postscript file with the help of Windows. The second step is to convert the postscript file to PDF format - this is where the real work is. As a user, you will never see these bits - just the final result as a PDF document.
Step 1 - The Common Denominator
It all starts with a postscript file. This is created when you use File-Print in MS Word, WordPerfect or any other source application and choose your favorite PDF application as the printer. The result is actually a Postscript file although you never see this. This process uses the existing Windows Printing software (part of Windows) to create the postscript file - in fact - your source application thinks its printing to paper.
Postscript files were originally designed to help postscript printers exactly recreate an electronic document on paper. Thus the perfect adaption of this type of printer-control-file for electronic paper which we call PDF.
Step 2 - Creating the PDF Document
The next step is to translate the postscript file commands into the equivalent (or something close to equivalent) to PDF commands. Basic conversions tend to be consistent from one PDF application to another although formatting variations and problems can creep in at this stage.
Once the basic conversion has been completed, some PDF applications will then try to improve the PDF. How is this possible if they're following the ISO standard? The standard defines the components and output format - not how a PDF is are assembled and that's the difference.
More sophisticated products will embed font information pulled from the computer's Windows font libraries - thus eliminating the need to manually embed fonts (sometimes required by a court or agency). Some products will optimize graphics by compressing them or by looking for repeating graphics which are then stored just once in the PDF document. The result is often a smaller more complete PDF document file.
I mentioned formatting problems - these occur when the PDF application has not done a good job of finding a PDF command(s) to match a series of postscript commands. The results can be PDF files which don't display correctly or worse.
The Bottom Line
I'm afraid you can't tell by looking. If you're having problems with filings or exchanging PDFs this may help you understand why. If you are considering a new PDF application, ask your provider about these issues - and test (test and test) samples with test-filings whenever possible.
The way a PDF file is created can make a difference. It can save you frustration and time - and what's more valuable than that?