How to fix slow PDF files

Written by william harrel
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How to fix slow PDF files
Optimise the images in slow PDFs (building Internet image by Danielle Bonardelle from Fotolia.com)

Acrobat's Portable Document Format (PDF) is designed to create multipurpose documents---documents designed for printing and for displaying on computers. An inherent problem in this approach to rendering PDFs is that documents designed for printing require images with much higher resolutions than documents designed for display on computer monitors. High-resolution images in PDFs create large files, often making downloading them from the Internet and navigating them in Acrobat Reader slow and cumbersome. You can fix large, slow PDFs with Acrobat Pro's PDF Optimizer.

Skill level:
Moderately Easy

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Things you need

  • Adobe Acrobat Pro 8 or later

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Instructions

  1. 1

    Open the slow PDF in Acrobat Pro. Click "File" on the menu bar and choose "Open." This displays the Open dialogue box. Navigate to the file, select it and then click "Open."

  2. 2

    Click "Advanced" on the menu bar and choose "PDF Optimizer." This opens the PDF Optimizer dialogue box.

  3. 3

    Click the "Audit space usage" button to open the Audit Space Usage dialogue box. This is an informational dialogue box. It displays the overall size (in bytes) of the elements making up the PDF and the percentage of the file size each type of element uses. For example, notice that "Images" takes up the largest percentage of the file, sometimes up to 80 per cent or more of the overall PDF size. Click "OK" to close the dialogue box.

  4. 4

    Examine the "Color Images" portion of the "Image Settings" section (the first section) of the PDF Optimizer dialogue box. Notice the field next to the "Downsample" drop-down. This is the resolution of the colour images in your PDF, measured in dots per inch (DPI). Computer monitors can display only 72 DPI or 96 DPI on High Definition (HD) monitors. If the value in the Resolution field is higher than 72 (or 96 for HD displays), change this number to optimise the images for display on computers. You can also make the images smaller by adjusting the compress quality (the "Quality" drop-down). Be careful though, setting this drop-down to a setting lower than "Medium" can greatly degrade your image quality.

  5. 5

    Examine the "Grayscale Images" portion of the "Image Settings" section (the second section) of the PDF Optimizer dialogue box. Notice the field next to the "Downsample" drop-down. This is the resolution of the grayscale images in your PDF. If the value in the Resolution field is higher than 72 (or 96 for HD displays), change this number to optimise the images for display on computers. You can also make the images smaller by adjusting the compress quality (the "Quality" drop-down). Setting this drop-down to a setting lower than "Medium" can also degrade your image quality.

  6. 6

    Examine the "Monochrome Images" portion of the "Image Settings" section (the third section) of the PDF Optimizer dialogue box. Notice the field next to the "Downsample" drop-down. This is the resolution of the monochrome images in your PDF. If the value in the Resolution field is higher than 72 (or 96 for HD displays), change this number to optimise the images for display on computers.

  7. 7

    Click "OK" to apply the settings. Acrobat Pro displays the "Save Optimized As" dialogue box. This is a safeguard, so that you don't inadvertently save over the original print-quality PDF. Rename the file in the "File name" field and click "Save." You now have a PDF optimised for the Internet.

Tips and warnings

  • InDesign and some other high-end design programs have an export setting for optimising PDFs. In InDesign, for example, you would choose "Smallest File Size" from the export options during the PDF export process.
  • Optimising PDFs for the Internet sometimes involves a trade-off between quality and file size. If, for example, your PDF users will download and print the document, setting image quality to 72 DPI can cause poor print quality, especially for monochrome images. You should set your DPI between the optimal print quality setting (300 DPI) and the optimal display quality (72 DPI). Set colour and grayscale images to about 150 DPI and monochrome images to 300 DPI. (Monochrome images are not very big, anyway.)

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