PDF Optimizer provides many settings for reducing the size of PDF files. Some of the PDF Optimizer settings are comparable to the settings that are available when you create a PDF file using Distiller. Whether you use all of these settings or only a few depends on how you intend to use the files and on the essential properties a file must have.
In most cases, the default settings are appropriate for maximum efficiency—saving space by removing embedded fonts, compressing images, and removing items from the file that are no longer needed. Before you optimize a file, it’s a good idea to audit the file’s space usage. The space audit results may give you ideas about where best to reduce file size. You can also reduce the size of your PDF by using the Reduce File Size command.
Some methods of compression may make images unusable in a print production workflow. You should experiment with various settings before making changes that can’t be discarded.
Auditing the space usage gives you a report of the total number of bytes used for specific document elements, including fonts, images, bookmarks, forms, named destinations, and comments, as well as the total file size. The results are reported both in bytes and as a percentage of the total file size.
You can also audit space usage of a PDF in the Content pane. Choose View > Show/Hide > Navigation Panes > Content. From the Content pane options menu , choose Audit Space Usage.
The Images panel of the PDF Optimizer lets you set options for color, grayscale, and monochrome image compression, and image downsampling.
Reduces file size by lowering the resolution of images, which involves merging the colors of original pixels into larger pixels.
Note: Masked images and images with a size less than 16-by-16 pixels are not downsampled.
Reduces file size by eliminating unnecessary pixel data. In general, JPEG and JPEG 2000 compression give better results on images like photographs with gradual transitions from color to color. ZIP is the better choice for illustrations with large areas of solid, flat color, or patterns made up of flat colors. For monochrome images, JBIG2 compression, which is available in PDF Optimizer but not in Distiller, and it is superior to CCITT.
Available only for JPEG and JPEG 2000 formats. JPEG and JPEG 2000 compression methods are typically lossy, a process that permanently removes some pixel data. You can apply lossy JPEG or JPEG 2000 compression to color images at various levels (Minimum, Low, Medium, High, Maximum). For JPEG 2000 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.
Available only for JPEG 2000 format. Divides the image being compressed into tiles of the given size. (If the image height or width is not an even multiple of the tile size, partial tiles are used on the edges.) Image data for each tile is individually compressed and can be individually decompressed. The default value of 256 is recommended.
Optimize Images Only If There Is A Reduction In Size
When selected, if the image setting will cause an increase in file size, the optimization for that image is skipped.
To ensure an exact match to the source document, it’s a good idea to embed all fonts used in the document. If you don’t need an exact match and you prefer a smaller file, you can choose not to embed fonts for roman text and East Asian text (Traditional Chinese, Simplified Chinese, Korean, and Japanese). Text in these languages is replaced with a substitution font when viewed on a system that does not have the original fonts. The Fonts panel of the PDF Optimizer contains two lists for fonts: fonts that are available for unembedding, and fonts to unembed. Certain fonts aren’t available for unembedding and don’t appear in the Fonts panel. To unembed fonts in a document, select one or more fonts in the Embedded Fonts list, and click the Unembed button. If you don’t want to embed subsets of the embedded fonts, deselect Subset All Embedded Fonts. To prevent unembedding for all fonts in the document, select Do Not Unembed Any Font.
If your PDF includes artwork that contains transparency, you can use presets in the Transparency panel of PDF Optimizer to flatten transparency and reduce file size. (Flattening incorporates transparency into corresponding artwork by sectioning it into vector-based areas and rasterized areas.) PDF Optimizer applies transparency options to all pages in the document before applying other optimization options.
If you select the Acrobat 4.0 And Later compatibility setting, the Transparency panel is enabled and all transparency in the file is flattened during optimization. This ensures compatibility with Acrobat 4.0 and earlier, which doesn’t support transparency.
When you create flattening presets, they appear with the default presets in the Transparency panel.
Transparency flattening cannot be undone after the file is saved.
The Discard Objects panel lets you specify objects to remove from the PDF and lets you optimize curved lines in CAD drawings. You can discard objects created in Acrobat and in other applications. Selecting an object removes all occurrences of that object within the PDF.
In the Discard Objects area, you can select from these and other options:
Discard All Form Submission, Import And Reset Actions
Disables all actions related to submitting or importing form data, and resets form fields. This option retains form objects to which actions are linked.
Flatten Form Fields
Makes form fields unusable with no change to their appearance. Form data is merged with the page to become page content.
Discard All Alternate Images
Removes all versions of an image except the one destined for on-screen viewing. Some PDFs include multiple versions of the same image for different purposes, such as low-resolution on-screen viewing and high-resolution printing.
Discard Embedded Page Thumbnails
Removes embedded page thumbnails. This is useful for large documents, which can take a long time to draw page thumbnails after you click the Page Thumbnails button.
Discard Document Tags
Removes tags from the document, which also removes the accessibility and reflow capabilities for the text.
Convert Smooth Lines To Curves
Reduces the number of control points used to build curves in CAD drawings, which results in smaller PDF files and faster on-screen rendering.
Detect And Merge Image Fragments
Looks for images or masks that are fragmented into thin slices and tries to merge the slices into a single image or mask.
Discard Embedded Print Settings
Removes embedded print settings, such as page scaling and duplex mode, from the document.
Use the Discard User Data panel to remove any personal information that you don’t want to distribute or share with others. If you’re unable to find personal information, it may be hidden. You can locate hidden text and user-related information by using the Examine Document command (Tools > Redact > Remove Hidden Information).
Discard All Comments, Forms And Multimedia
Removes all comments, forms, form fields, and multimedia from the PDF.
Discard Document Information And Metadata
Removes information in the document information dictionary and all metadata streams. (Use the Save As command to restore metadata streams to a copy of the PDF.)
Discard All Object Data
Removes all objects from the PDF.
Discard File Attachments
Removes all file attachments, including attachments added to the PDF as comments. (PDF Optimizer doesn’t optimize attached files.)
Discard External Cross References
Removes links to other documents. Links that jump to other locations within the PDF are not removed.
Discard Private Data Of Other Applications
Strips information from a PDF document that is useful only to the application that created the document. This does not affect the functionality of the PDF, but it does decrease the file size.
Discard Hidden Layer Content And Flatten Visible Layers
Decreases file size. The optimized document looks like the original PDF but doesn’t contain any layer information.
The options in the Clean Up panel of the PDF Optimizer dialog box allow you to remove useless items from the document. These items include elements that are obsolete or unnecessary for your intended use of the document. Removing certain elements can 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, use the default selections.
Use Flate To Encode Streams That Are Not Encoded
Applies Flate compression to all streams that aren’t encoded.
In Streams That Use LZW Encoding, Use Flate Instead
Applies Flate compression to all content streams and images that use LZW encoding.
Discard Invalid Bookmarks
Removes bookmarks that point to pages in the document that have been deleted.
Discard Unreferenced Named Destinations
Removes named destinations that are not being referenced internally from within the PDF document. Because this option does not check for links from other PDF files or websites, it does not fit in some workflows.
Optimize Page Content
Converts all end-of-line characters to space characters, which improves Flate compression.
Optimize The PDF For Fast Web View
Restructures a PDF document for page-at-a-time downloading (byte-serving) from web servers.
Fast Web View restructures a PDF document for page-at-a-time downloading (byte-serving) from web servers. With Fast Web View, the web server sends only the requested page, rather than the entire PDF. This option is especially important with large documents that can take a long time to download from a server.
Check with your webmaster to make sure that the web server software you use supports page-at-a-time downloading. To ensure that the PDF documents on your website appear in older browsers, you can also create HTML links (versus ASP scripts or the POST method) to the PDF documents and use relatively short path names (256 characters or fewer).
Follow this procedure to make sure that you have Acrobat set up to enable Fast Web View during the PDF creation process.
Use this procedure after you have verified your Fast Web View Preferences setting and checked the PDF properties to be sure that the file is not already enabled for Fast Web View.
In Acrobat Pro, you can also quickly enable Fast Web View in entire folders of Adobe PDF files by using the Prepare for Web Publishing action. See Run an action.