Compress a PDF File

Portable Document Format (PDF) files are the open, standard way to deliver documents electronically. Supported by virtually any platform—Windows, Mac OS, Linux—converted PDF documents, graphics, charts, and forms look exactly as they would if they were printed. At times, it is necessary to compress these files to be able to send them as email attachments or upload them to websites. There are many options for compressing PDF files, here are some.

Steps

Online Compression Tools

  1. Locate an online PDF compression tool. This may be found by typing the following search terms into your preferred web browser: “free online PDF compression.” Ensure that the service is free, and comes recommended by one of the large, well-known computer or business print or online publications (There tend to be highly visible website banners indicating that the site received kudos from a reputable source).
  2. Either select the file you want to compress from your computer, or drag and drop it to begin the upload. The website may have you watch an ad or type in a captcha code.
  3. Wait. Once compression is complete, you will be alerted that the download is available. Some services email you the compressed document, while others allow you to download it directly from the site.

Adobe Acrobat

  1. Open your PDF in Adobe Acrobat. You may also select more than one PDF in a PDF Portfolio.
  2. Click File → Save As → Reduced Size PDF. Select the version of compatibility needed. If you can ensure that all users will be using version Adobe Acrobat X or later, the file will be further compressed.[1]

Preview (Mac OS)

  1. Open your PDF in Preview by double-clicking on it in the Finder menu.
    • By default, PDF files open in Preview unless you have Adobe Reader or a third party PDF viewer. If that is the case, simply locate the PDF, right click it, click “Open With” and choose Preview.
  2. Click File → Export. A dialog box will appear.
  3. Click the Quartz Filter option and select “Reduce File Size”.
  4. Click “Save”. If you do not rename this file, a dialog box will appear asking if you wish to replace the original document. This will overwrite the current document.[2]

Adobe Acrobat’s PDF Optimizer

  1. Select PDF Optimizer from the Advanced menu in Adobe Acrobat. The PDF Optimizer window will appear and will present you with a number of options for file compression.
  2. Determine which items are increasing the file size. Click on the “Audit space usage” button at the top right of the window. Here you will be shown the different components of your documents (fonts, color, etc.), the number of bytes used, and the percentage of space being utilized by each component. Decide what components could be trimmed back and navigate through the corresponding panels by clicking on them on the left of the screen.
  3. Select the Images Settings Panel to make adjustments to images in your document. Here you can adjust settings for color, grayscale, and monochrome image compression.
    • The higher the pixels per inch (ppi), the better the image resolution. If you are not printing, consider using a reduced ppi (which will make you file smaller). For on-screen viewing, you only need 72 ppi.
    • Downsampling reduces the resolution of images by decreasing the number of pixels by merging original pixel colors into larger pixels. Choose from the option in the drop-down. “Average Downsampling to” averages the pixels in a sample area and applies that color to the entire area. “Subsampling to” selects a pixel in the center of the sample and applies that color to the entire area. “Bicubic Downsampling to” uses a weighted average to determine pixel color. This option yields smoother gradations.
  4. Click on the Fonts Settings Panel to either embed or unembed your fonts. Embedding fonts from your original document ensures that, if opened on another computer, the fonts in your PDF will be able to be seen and printed even if that computer does not contain the original font.
    • If you do not require the exact font in your PDF, you can choose not to embed the fonts, making the file smaller. The fonts will automatically be replaced on systems that do not contain the fonts used in the original. Two columns in this panel (“Embedded Fonts” and “Font to Embed”) allow you to choose accordingly.
  5. Select the Transparency Setting Panel to adjust transparencies levels in artwork contained in your document. Drop-down options include “Low Resolution”, “Medium Resolution”, and “High Resolution” and each contains a corresponding group of presets that affect the transparency level, gradient and meshes, etc. Adjusting the transparency resolution here will reduce file size.
  6. Choose the Discard Objects Panel to eliminate unnecessary items from the document. When you open this panel, you will see a list of Discard Object Settings, and a checklist. Settings here include “Discard all form submissions”, “Discard documents tags”, “Discard bookmarks”, etc. Simply click to select the objects that do not apply to the original document.
  7. Click on the Discard User Panel to remove personal information from your document. As with the Discard Objects Panel, this panel lists Discard User related information next to a checklist. Select from options such as “Discard all comments”, “Forms and multimedia”, and “Discard private data of other applications”, among others.
    • Personal information may be hidden. To locate it, use the Examine Document command (Document→Examine Document).
  8. Choose the Clean Up Settings Panel to remove extraneous, useless data from your document. Make sure the “Compress document structure” is selected in the Object compression options drop-down.
    • By default, only elements that do not affect PDF functionality are selected. Choosing non-default settings may severely impact the functionality of the document, so it is recommended that you do not alter the settings unless you are sure you know what they’ll do.
  9. Click “OK” when you are done changing your settings. A window will appear prompting you to “Save Optimized As.” Select a file name, the location where you’d like it saved, and the format (PDF).[3]

Tips

  • Using only one font throughout the file will help reduce the file size, since the fonts are stored in the file's information.
  • Transparency flattening cannot be undone after the file is saved.

Related Articles

Sources and Citations

  1. ↑ http://help.adobe.com/en_US/acrobat/X/pro/using/WSFCDFBF6D-795A-4364-BA93-BB157AAD53ED.w.html
  2. ↑ http://support.apple.com/kb/PH7252
  3. ↑ http://help.adobe.com/en_US/photoshop/cs/using/WS23B45D06-1977-4006-8BEB-2DBB08CA502Ea.html
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