Last changed
11 Feb 1998 ............... Length about 1,000 words (6,000 bytes).
This is a WWW document by Steve Draper, installed at http://www.psy.gla.ac.uk/~steve/acrobat.html.
You may copy it.
How to refer to it.
Acrobat readers
A new web document format is becoming widespread, known as PDF format.
To read these documents, you need a free Acrobat reader from Adobe, unless
your machine already has one. Student cluster machines at Glasgow university
do now have one as standard.
To get one, download one from Adobe.
Or you if you want a version 3 one for the Macintosh from this site, ftp here.
PDF format & Acrobat readers: Is it a good idea?
PDF is a new document format, becoming widely used in conjunction with the
WWW. The format is related to postscript, but uses all 8 bits plus
compression. It is promoted by Adobe. You can get a free viewer software
from them, so everyone can fairly easily read PDF documents. They hope to
make money from authoring software. However you can get free software to
create PDF from postscript.
PDF files often look bleary, blurry, smeary on screen. I don't know why, but
probably to do with the fonts specified in the original document and not done
well by the viewer.
Main features of PDF
- File compression, to keep file sizes and hence download times down: see
section below.
- Combines text and graphics, so may seem more convenient than HTML to
authors.
- (Often) Easy creation of a PDF version from any application program.
(You can create a PDF version of a document easily if you have a postscript
version; and since many printers now expect postscript, many people can
generate postscript files from all their application programs.)
- It preserves a WYSIWYG format i.e. the appearance on the page created by
the original application.
This means that if you want to distribute a printed document via the web,
for users to print locally but also with an option of viewing it on-line,
then PDF is a convenient route for many although not all people. But
if the document is meant primarily for viewing on the web, then there are
objections:
Why it is bad for primary web pages
- Despite the viewer software being free, not everyone has one. It can
take hours of effort for someone who is unlucky or not used to downloading and
installing software to get a viewer. And some may not be able to do this.
Using PDF cuts you off from some of the WWW audience.
- It does WYSIWYG presentation i.e. the final appearance will at best look
exactly like what the author created. This is in fundamental contravention
of one of the basic ideas of the WWW, which is to give the user control
through their browser over how documents look. You will force them to use
your preferred appearances. Since you are probably not an expert on
readability (do you use Times font in your browser, despite the experimental
results?), and do not know what their eyesight is like, nor what size their
screen is etc. etc., you will provide an annoyingly downgraded experience for
a significant proportion of your audience.
So what is it good for?
- Distributing documents via the WWW for local printing. YES.
Advantages: compressed format; can be printed by non-postscript printers
via the PDF viewer. Unlike HTML, author can do page layout for user. But
watch the A4 / US letter problem.
- Putting OHP slides on the WWW. YES.
- Web pages meant for web use. NO.
Violates end user control over appearance.
Use at University of Glasgow
The university has adopted it as a standard facility, so PDF viewers will be
on the cluster machines undergraduates use: you can rely on this. Furthermore
those clusters do not have a facility for printing postscript files, so you
can't distribute documents that way.
It is probably not a good idea to use it as an alternative to handouts: it
will just cost more and block up public equipment if all your students are
going to want or need a paper copy.
It probably is a good way to put reminder copies of OHPs etc. on the web at
little effort to yourself.
It probably is not a good way to author web pages.
How to create PDF documents for the web
These instructions will work, at least for Mac users.
- Author the document using any favourite application program
- Use printing software to create a postscript version.
- On the Mac, if you
have the current laserwriter8 print drivers, then the print command brings up
an option "Destination" of either printer or file: selecting file lets you
generate a postscript file.
- Note that if your page size setting was A4 when you first create the
postscript file, then that seems to get frozen in. If your end user has US
letter paper, then they will get the bottom clipped off all the pages, and the
PDF viewer doesn't seem able to help with that.
This probably means that UK authors should always create US letter format
print images at this point.
- Use either Adobe software or else the free Ghost software to create a
PDF file from the postscript one.
- Place it on the web (as a .pdf file, with a link pointing to it).
Getting PDF creation software
You can buy Adobe's software: Adobe's web site
Aladdin Ghostscript software is great, free at least to academics, and
available on the net. It is both a postscript viewer AND PDF conversion.
However, I have recently found it does VERY badly at converting
postscript files with any graphics at all in. Selecting options in the print
dialogue used to create the postscript file to force downloading of all fonts
used helps a bit, but does not solve the graphics problem.
Aladdin Ghostscript: Mac users begin here
Aladdin Ghostscript: Others could begin here.
Demo PDF document
File sizes / download times
PDF uses 8 bits (not 7 bit ascii like postscript) and file compression,
which can reduce download time. This seems to make it competitive with HTML,
and certainly much better than postscript files for size and hence download
times.
Here is a table concerning a test text file.
| File type |
File size (bytes) |
File size (Relative) |
| Ascii text |
5587 |
1 |
| HTML |
6000 |
1.07 |
| Word |
13,598 |
2.43 |
| Postscript |
14,581 |
2.61 |
| PDF |
5,219 |
0.93 |