PDF compatibility levels

When you create PDFs, you must decide which PDF version to use. You can change the PDF version by switching to a different preset or choosing a compatibility option when you save as PDF or edit a PDF preset.

Generally speaking, unless there’s a specific need for backward compatibility, you should use the most recent version (in this case version 1.7). The latest version will include all the newest features and functionality. If you’re creating documents to be distributed widely, choose Acrobat 5.0 (PDF 1.4), or Acrobat 6.0 (PDF 1.5) so users can view and print the document.

The following table compares some of the functionality in PDFs created using the different compatibility settings.

Share custom PDF settings

You can save and reuse your own Adobe PDF preset definitions. Share a custom preset by sending a copy of the resulting file to other users to add to Distiller apps installed on their computers.

PDF settings files have the extension .joboptions. Custom preset files are stored in the following locations.

• Windows 11 (64-bit), Windows 10 version 1810 or later (32-bit and 64-bit), Windows 8, 8.1 (32-bit and 64-bit)†, Windows 7 SP1 (32-bit and 64-bit), or Windows Server - 2008 R2 (64 bit), 2012 (64 bit), 2012 R2 (64 bit)†, 2016 (64 bit), or 2019 (64 bit) Users/User/AppData/Roaming/Adobe/Adobe PDF/Settings
  

• (Acrobat Pro for macOS) User/[username]/Library/Application Support/Adobe/Adobe PDF/Settings

The settings file appears as the selected option in the Default Settings menu.

Compressing and downsampling images

When converting PostScript files to PDF, you can compress vector objects (such as text and line art) and compress and downsample images. Line art is described with a mathematical equation and is usually created with a drawing program such as Adobe Illustrator. Images—whether color, monochrome, or grayscale—are described as pixels and are created with applications like Adobe Photoshop or by scanning. Monochrome images include most black-and-white illustrations made by paint programs and any images scanned with an image depth of 1 bit.

When you downsample (or decrease the number of pixels), information is deleted from the image. With Distiller, you specify an interpolation method—average downsampling, bicubic downsampling, or subsampling—to determine how pixels are deleted. Depending on the settings you choose, compression and downsampling can significantly reduce the size of a PDF with little or no loss of detail and precision.

When Distiller processes a file, it normally applies the compression settings to images throughout the file. However, you can assign different compression and downsampling methods to individual images.

Varying the compression and downsampling methods within a PDF

Before you create a PDF, you can take various approaches to applying different compression and downsampling options to the individual images that will go into that PDF:

• Use Adobe Photoshop CC to resample and compress existing image files before using Distiller. When you are ready to create the PDF in Distiller, be careful to deselect the compression and downsampling or subsampling options.

• Create separate PostScript files for each part of the document that you want to process differently, and use different compression options to distil each part. Then use Distiller to merge the files into a single PDF.

• When you create color, grayscale, and monochrome images in an art application (such as Adobe Photoshop CC), select the compression and downsampling settings that you want when you save each image from within that application.

• Insert Distiller parameters before images in a PostScript file. You can use this technique to process every image in a document differently. This technique is the most difficult because it requires knowledge of PostScript programming. For more information on using parameters, see the SDK documentation on the Acrobat Developer Center at https://opensource.adobe.com/dc-acrobat-sdk-docs/acrobatsdk/ (English only).

Compression methods

Distiller applies ZIP compression to text and line art, ZIP or JPEG compression to color and grayscale images, and ZIP, CCITT Group 3 or 4, or Run Length compression to monochrome images.

You can choose from the following compression methods:

ZIP Works well on images with large areas of single colors or repeating patterns, and for black-and-white images that contain repeating patterns. Acrobat supports only 8-bit ZIP compression, which is lossless; that is, data is not removed to reduce file size, so image quality is not affected.

JPEG Suitable for grayscale or color images, such as continuous-tone photographs. JPEG is lossy, which means that it removes image data and may reduce image quality. However, it attempts to reduce file size with the minimum loss of information. Because JPEG compression eliminates data, it can achieve much smaller file sizes than ZIP compression.

CCITT Available only for monochrome bitmap images. CCITT (Consultative Committee on International Telegraphy and Telephony) compression is appropriate for black-and-white images and any images scanned with an image depth of 1 bit. Group 4 is a general-purpose method that produces good compression for most monochrome images. Group 3, used by most fax machines, compresses monochrome images one row at a time.

Run Length Produces the best results for images that contain large areas of solid white or black.