To best
serve your readers, you should ensure that your PDF is compatible
with their viewers. What PDF viewers are they running? Assume that
they have at least upgraded to the previous
version of Acrobat/Reader (or another, compatible viewer). PDFs
created with the newest Acrobat might be
incompatible with previous versions. A little care can prevent
inconveniences to your readers such as the one shown in .
Figure 1. Messages that annoy readers
PDF Versions Overview
With each new version of
Acrobat, Adobe introduces an updated
version of the PDF specification. They go together, as shown in .
Table 1. Acrobat version information
Acrobat version | Year introduced | PDF version |
|---|
3.0 | 1996 | 1.2 |
4.0 | 1999 | 1.3 |
5.0 | 2001 | 1.4 |
6.0 | 2003 | 1.5 |
In many cases, an older viewer still can read a newer-version PDF
(although the viewer will complain). Its behavior depends on which
new features the PDF uses. Which viewers implement newer features?
Here are some highlights, selected for their bearing on mass
distribution. For complete details, consult the PDF Reference,
Versions 1.3, 1.4, and 1.5.
- PDF 1.3 (Acrobat 4) introduced:
Digital signatures
File attachments
JavaScript support
Logical page numbering
- PDF 1.4 (Acrobat 5) introduced:
Additional 128-bit encryption option
Additional JavaScript trigger events (document close, will save, did
save, will print, did print)
Enhanced interactive forms
- PDF 1.5 (Acrobat 6) introduced:
An older viewer can simply ignore many of the things it
doesn't understand. The showstoppers are the
compression or encryption features, because the viewer
can't show the document if it can't
read the streams.
TIP
If your PDF relies on newer JavaScript or forms features to work
properly, prevent older viewers from opening your PDF. Determine the
minimum PDF version your document requires and then apply the
corresponding encryption using an empty password .
Older viewers simply won't be able to read it.
Create Compatible PDFs
Out of the box,
Distiller or
PDFMaker yields PDFs that are compatible with the
previous version of Acrobat. No problem.
When you open a PDF in Acrobat, modify it, and then save it, your
PDF's version is upgraded silently to match
Acrobat's. It is no longer compatible with the
previous versions of Acrobat/Reader. This happens regardless of
whether your PDF uses any of the new features.
TIP
Install older versions of Acrobat Reader and test your PDFs, if you
are worried about how they'll look or function.
Download old installers from http://www.adobe.com/products/acrobat/reader_archive.html
or http://www.oldversion.com/program.php?n=acrobat.
One solution is to use the Reduce File Size feature in
Acrobat 6 (File → Reduce File Size . . . →
Compatible with: Acrobat 5.0 and later), which enables you to also
set the compatibility level of the resulting PDF. Another solution is
to use the PDF Optimizer feature (Advanced → PDF Optimizer .
. . ) and set the "Compatible with"
field to "Acrobat 5.0 and later." A
third option is to refry your PDF .
