OPTIMIZING PDFS WITH ACROBAT PRO 8
GUIDELINES FOR CREATING PDF DOCUMENTS THAT ARE SMALLER IN FILE SIZE
INTRODUCTION
If you incorporate a lot of images in a file and then convert it to a PDF, the file size may be
quite large if the images were not compressed prior to placing them in your original document.
You can strip, flatten, downsample resolutions, and remove features from your PDF in order to
minimize its file size. This tutorial will lead you through the steps to compress your PDF.
REDUCING FILE SIZE THE EASY WAY WITH THE REDUCE FILE SIZE COMMAND
Reducing the size of a PDF in Acrobat Pro with the Reduce File Size command can improve
its access time on the web without greatly altering its appearance. The Reduce File Size
command will resample and recompress images, remove embedded fonts, compress the
document structure, and clean up some other elements. Note: If the file size is already as
small as possible, this command will have no effect whatsoever.
To reduce your file with this method, open your PDF document in Adobe Acrobat Professional 8
(not Adobe Reader) and then choose Document > Reduce File Size.
When the Reduce File Size dialog box appears, select the version compatibility that you
need, and click OK. Limiting compatibility to the latest version will allow for a greater
reduction in the file size but may limit the number of users that can access your
document. We suggest making your document at least backwards compatible with Acrobat
version 6.0 or later.
Figure 1: Reduce File Size Dialog Box
CONTROLLING SPECIFIC ELEMENTS WITH THE PDF OPTIMIZER COMMAND
1.
If you want to control the optimization changes more exactly, use the PDF Optimizer
instead. To do this, begin by opening your PDF file in Adobe Acrobat Professional 8 and
selecting Advanced > PDF Optimizer.
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Figure 2: Advanced > PDF Optimizer Selection in Acrobat Pro 8
2.
When the PDF Optimizer dialog box appears, click on the Audit space usage… button.
Figure 3: Audit space usage… button
3.
The Audit Space Usage dialog box appears displaying the amount of bytes of each
element in your document and the percentage of total file size that these elements take
up. Focus your efforts on slimming down the components of your PDF that are taking up
the most space. In our case, the illustration below shows that images are taking up the
most space in our PDF, with content streams (text) and fonts being the runner-ups in
terms of the amount of space they require within the total file size.
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Figure 4: Audit Space Usage Dialog Box
4.
When you are finished reviewing it, click the OK button to close the Audit Space Usage
dialog box and return to the PDF Optimizer dialog box.
5.
When you first take a look at the PDF Optimizer dialog box, you will see that the
Settings: pull-down menu is set to Standard; it displays the current version of the PDF
you are trying optimize; and the Make compatible with: pull-down menu will say Retain
Existing. Change the pull-down menu next to Make compatible with: to Acrobat 6.0
and later. Once you do this, you will see that the Settings: pull-down menu
automatically changes to Custom.
6.
The first option in the PDF Optimizer dialog box is Images. If your PDF is intended
primarily for web use rather than print use, you can save a lot of space by manipulating
the downsampling and compression values of the images. If you want your PDF to print
the images with the same resolution in which you made the document, do not continue
with optimizing the images as discussed below.
7.
Before we continue, it is important that you understand the terms downsample,
compression, and quality that Acrobat Pro refers to in this dialog box:
Downsampling reduces the file size by lowering the resolution of the images, which
involves merging the colors of original pixels into larger pixels
Compression reduces the file size by eliminating unnecessary pixel data (In general, JPEG
and JPEG2000 compression give better results on images like photographs with gradual
transitions from color to color). If you use Acrobat 6 compatibility mode or higher you can
use JPEG2000, which is slightly more efficient than JPEG compression. ZIP is the best
choice for illustrations with large areas of solid, flat color or patterns made up of flat
colors; and for monochrome images, JBIG2 compression is the best choice.
Quality can only be set in the PDF Optimizer for JPEG and JPEG2000 compression. JPEG
and JPEG2000 compression methods are typically lossy, a process that permanently
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removes some pixel data. You can apply lossy JPEG or JPEG2000 compression to color
images at various levels (minimum, low, medium, high, maximum). For JPEG2000
compression, you can also specify lossless so that no pixel data is removed. Compression
for monochrome images is lossless, except for JBIG2 compression, which provides both
lossy and lossless modes of compression.
With these terms in mind, please review Figures 5, 6, and 7 below for the settings that we
suggest you implement when optimizing your PDF for the web:
Figure 5: Suggested Image Optimization Settings for Color Images
Figure 6: Suggested Image Optimization Settings for Grayscale Images
Figure 7: Suggested Image Optimization Settings for Monochrome Images
8.
Once you change these image optimization settings, you can save them for future use by
clicking the Save button in the upper part of this PDF Optimizer dialog box and providing
a name for your settings such as “Best PDF Image Optimization for the Web.” You’ll see
the Settings: pull-down menu change to the name you saved and in the future, you can
just select it when you open the PDF Optimizer dialog box and not have to do all this
again.
9.
Now we need to consider how to optimize the fonts. Embedding fonts ensures that your
document will be rendered exactly as you intended for it to look, but it bulks up your PDF
somewhat. If you don’t embed your fonts and Acrobat cannot find the fonts you used, it
will substitute similar fonts for you. Note that Adobe requires that all PDF applications
include the so-called BASE 14 set of standard fonts that can be used without embedding,
that is: the fonts in the four faces of Courier, Helvetica, and Times plus Symbol and ITC
Zapf Dingbats. Thus, if you use fonts from the BASE 14 set of basic fonts found on most
computers you can safely choose to NOT embed your fonts provided your readers are on
Windows NT/2K/XP or Mac OS X using Adobe Acrobat. Note: If you are using any
symbols, international glyphs, or non-roman languages then you must embed your fonts
for these characters to appear properly in your document.
10. To unembed fonts in a document, select one or more fonts in the Embedded Fonts list,
and click the Unembed button. If you change your mind about unembedding a font,
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select it in the list on the right and click the Retain button.
11. Transparency Options: If your PDF includes artwork that contains transparency, you can
use presets in the Transparency panel of the PDF Optimizer to flatten transparency and
reduce the file size. Flattening incorporates transparency into corresponding artwork by
sectioning it into vector-based areas and rasterized areas. The options in this area will be
grayed out if you don’t have any images that contain transparency. Note that PDF
Optimizer will apply transparency options to all pages in the document before applying
the other optimization options.
12. In the Discard Objects panel you can remove features that you don't use from your PDF
as well as optimize curved lines in CAD drawings. We suggest that you select the following
choices as illustrated in Figure 8: Discard all alternate images: This removes all
versions of an image except the one destined for on-screen viewing since some PDFs
include multiple versions of the same image for different purposes, such as low-resolution
on-screen viewing vs. high-resolution printing; Convert smooth lines to curves: This
reduces the number of control points used to build curves in CAD drawings, which results
in smaller PDF files and faster on-screen rendering; and Discard embedded print
settings: This removes embedded print settings, such as page scaling and duplex mode,
from the document.
Figure 8: Discard Objects Settings
NOTE: DO NOT DISCARD THE DOCUMENT TAGS. CAL POLY REQUIRES THAT ALL DIGITALLY POSTED
DOCUMENTS BE ACCESSIBLE AND REMOVING THE TAGS FROM THE DOCUMENT WILL MAKE IT INACCESSIBLE
AND ALSO EFFECT THE REFLOW.
13. The Discard User Data panel allows you to remove personal information you don't want
to share with others. You can locate hidden text and user-related information by going
to Document > Examine Document.
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Figure 9: Discard User Related Information
14. The Clean Up panel options of the PDF Optimizer removes useless items from the
document. These items include elements that are obsolete or unnecessary to your
intended use of the document. Be aware that removing certain elements may seriously
affect the functionality of the PDF. By default, only elements that do not affect
functionality are selected. If you are unsure of the implications of removing other options,
you should use the default selections as displayed below in Figure 10.
Figure 10: Clean Up Settings
15. Now click OK to apply the settings you selected in the PDF Optimizer and save out the file
when the Save Optimized As… dialog box appears. Save under a different name if you
wish to compare its size with your original version.
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