Optimizing PDFs

Acrobat reduces the size of a PDF file without compromising quality. The Acrobat PDF compression tool balances an optimized file size against the expected quality of images, fonts, and other file content.

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. You can use all of these settings or only a few. It depends on how you intend to use the files and the essential properties a file must have.

Usually, the default settings are suitable for achieving maximum efficiency. It includes saving space by removing embedded fonts, compressing images, and removing redundant items from the file. Before optimizing a file, it’s a good idea to audit its space usage. The space audit results may provide insights into the possibilities of reducing file size. You can also reduce the size of your PDF by using the Reduce File Size command.

Audit the space usage of a PDF (Acrobat Pro)

The space usage audit reports the total number of bytes used for specific document elements. It includes fonts, images, bookmarks, forms, named destinations, comments, and the total file size. The results are reported in bytes and as a percentage of the total file size.

Optimize a PDF (Acrobat Pro)

PDF Optimizer options (Acrobat Pro)

Use the options from the panels in the PDF Optimizer dialog box to reduce the size of a PDF.

Images panel

The Images panel of the PDF Optimizer lets you set options for color, grayscale, and monochrome image compression, and image downsampling.

Specify the following options, as needed:

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 aren't downsampled.

Reduces file size by eliminating unnecessary pixel data. In general, JPEG and JPEG 2000 compressions yield better results on images, such as photographs with gradual transitions from color to color. ZIP is the better choice for illustrations with large areas of solid, flat colors, or patterns of flat colors. For monochrome images, JBIG2 compression is available in PDF Optimizer but not in Distiller, and it's 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 isn't 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.

When selected, if the image setting will cause an increase in file size, the optimization for that image is skipped.

Fonts panel

To ensure an exact match to the source document, embed all fonts used. If you don’t require an exact match and prefer a smaller file, skip embedding fonts for Roman 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 without original fonts. The Fonts panel of the PDF Optimizer contains two lists for fonts: fonts that are available for unembedding and fonts to unembed. Specific fonts aren’t available for unembedding and don’t appear in the Fonts panel. Select one or more fonts in a document in the Embedded Fonts list and select the Unembed button to unembed fonts in a document. If you don’t want to embed subsets of the embedded fonts, deselect Subset All Embedded Fonts. Select Do Not Unembed Any Font to prevent unembedding for all fonts in the document.
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Transparency panel

If your PDF includes artwork with transparency, 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. It 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.

Discard Objects panel

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:

Disables all actions related to submitting or importing form data, and resets form fields. This option retains form objects to which actions are linked.

Makes form fields unusable with no change to their look and feel. Form data is merged with the page to become page content.

Removes any actions in the PDF that use JavaScript.

Removes all versions of an image except the one destined for onscreen viewing. Some PDFs include multiple versions of the same image for different purposes, such as low-resolution onscreen viewing and high-resolution printing.

Removes embedded page thumbnails. It's useful for large documents, which can take a long time to draw page thumbnails after you select the Page Thumbnails button.

Removes tags from the document, which also removes the accessibility and reflow capabilities for the text.

Reduces the number of control points used to build curves in CAD drawings, which result in smaller PDF files and faster onscreen rendering.

Looks for images or masks that are fragmented into thin slices and tries to merge the slices into a single image or mask.

Removes embedded print settings, such as page scaling and duplex mode, from the document.

Removes embedded search indexes, which reduces the file size.

Removes all bookmarks from the document.

Discard User Data panel

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 (All tools > Redact a PDF > Sanitize Document, and then choose to 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 aren't removed.

Discard private data of other applications

Strips information from a PDF document that is useful only to the application that created the document. It doesn't 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 contains no layer information.

Clean Up panel

The options in the Clean Up panel of the PDF Optimizer dialog let you remove redundant items from the document. It includes obsolete or unnecessary elements for your intended use of the document. Removing certain elements can seriously affect the functionality of the PDF. By default, only elements that don't affect functionality are selected. Use the default selections if you're unsure of the implications of removing other options.

Specifies how to apply Flate compression in the file.

Applies Flate compression to all streams that aren’t encoded.

Applies Flate compression to all content streams and images that use LZW encoding.

Removes bookmarks that point to pages in the document that have been deleted.

Removes links that jump to invalid destinations.

Removes named destinations not referenced internally from within the PDF document. Because this option doesn't check for links from other PDF files or websites, it doesn't fit in some workflows.

Converts all the end-of-line characters to spaces, which improves Flate compression.

Restructures a PDF document for page-at-a-time downloading (byte-serving) from web servers.

Enable Fast Web View in a PDF

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 ensure the web server software supports page-at-a-time downloading. To ensure that the PDF documents on your website appear in older browsers, create HTML links (versus ASP scripts or the POST method) to the documents. Also, use shorter path names (256 characters or fewer).

Verify that an existing PDF is enabled for Fast Web View

Verify the Fast Web View Preferences setting

Follow this procedure to make sure that you have Acrobat set up to enable Fast Web View during the PDF creation process.

Enable Fast Web View for an existing PDF

Use this procedure after you've verified your Fast Web View Preferences setting and checked the PDF properties to ensure the file isn't already enabled for Fast Web View.