How to Optimize PDF File Size in Adobe Acrobat Reader

Edited 3 weeks ago by ExtremeHow Editorial Team

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PDF, or Portable Document Format, is a file format that captures all the elements of a printed document as an electronic image that you can view, navigate, print, or forward to someone else. PDFs are commonly used for documents because they preserve formatting and can be easily shared across different platforms without any changes. However, sometimes these PDF files can be quite large, which can be problematic for storage and sharing via email or other platforms with file size limitations. Fortunately, there are many ways to optimize and reduce the size of PDF files using Adobe Acrobat Reader. This lesson will walk you through different ways to optimize your PDF file size without losing quality.

1. Understanding PDF file size

Before we dive into optimization techniques, it's important to understand why your PDF files might be large. Several factors contribute to the size of a PDF:

• Images: High-resolution images, such as photographs and detailed graphics, can significantly increase the size of a PDF.
• Fonts: Embedded fonts, especially if they are custom or unusual, can make a PDF larger.
• Multimedia elements: Having video or audio files in a PDF will increase its size.
• Complex vector graphics: Complex images or vector graphics require more data, making the file size larger.
• Annotations and forms: Comments, form fields, and other annotations can also increase file size, although usually to a lesser extent than images or multimedia elements.

2. Techniques to optimize PDF file size

Now, let's explore different methods for optimizing the file size of PDF documents using Adobe Acrobat Reader. Each technique addresses different elements that increase file size, so you may need to use a combination of them for best results.

2.1. Using the "Save As" command

An easy step to reduce the size of a PDF is to use the "Save As" command, not just click "Save As." When you use "Save As," Adobe Acrobat Reader rewrites the entire PDF file structure, often resulting in a smaller file size by removing unnecessary elements or redundancies.

1. Open your PDF document in Adobe Acrobat Reader.
2. Export your file by clicking File > Save As.
3. Choose a location to save your PDF and give it a new name if necessary.
4. Click Save to create a new version of the document.

2.2. Reduce file size using the built-in feature

Adobe Acrobat has a built-in feature called "Reduce File Size" designed to efficiently compress a PDF document. This tool removes unnecessary elements, such as embedded fonts and unused objects, so that file space usage is minimized.

1. Open the PDF file in Adobe Acrobat.
2. Go to File > Save As Other > Reduced Size PDF.
3. In the Options dialog, you'll see a few settings for changing compatibility settings. Unless you need backward compatibility with earlier versions of Acrobat, it's generally recommended to select "Keep existing."
4. Click OK.
5. Choose a location to save your customized PDF and click Save.

This method is very effective for reducing the size of large documents, but it can compress images and reduce their quality, so it is important to check the final document before using or distributing it.

2.3. Audit the PDF for optimization

Adobe Acrobat enables you to analyze your PDF to understand which elements are contributing to its size. By auditing a PDF, you can more effectively identify and resolve size-related problems.

1. Open your PDF with Adobe Acrobat Pro (Note: this feature is only available in the Pro version).
2. Choose File > Save As Other > Optimized PDF.
3. In the "PDF Optimizer" window, select Audit Space Usage on the upper right corner.
4. Review the displayed results to see which components (images, fonts, etc.) take up the most space.

Once you've analyzed the file, proceed with more targeted optimizations according to the audit report, such as reducing image sizes, removing unwanted elements, or flattening form fields.

2.4. Optimizing the images in your PDF

Typically, images in a PDF take up a lot of space. You can optimize them by adjusting their resolution and compression settings.

1. In Adobe Acrobat Pro, open your PDF and choose File > Save As Other > Optimized PDF.
2. In the "PDF Optimizer" dialog, go to the "Images" section.
3. You can see options for downsampling images and changing the compression type. For example, you can choose "Bicubic Downsampling" and specify a low resolution (e.g., 150 dpi), and choose "JPEG" or "JPEG2000" compression with a medium quality setting.
4. After making adjustments, click OK to save the changes.

You can choose the extent of the changes based on your quality requirements and file size goals. It is often useful to make incremental adjustments and check the status of your document after each change.

2.5. Flatten PDF layers

Some PDF files contain many layers which can make them large. Although layers can be useful for separating content in complex documents, they can be flattened when not needed to reduce file size.

1. Open your PDF in Adobe Acrobat Pro.
2. Go to File > Save As Other > Optimized PDF.
3. In the "PDF Optimizer" dialog, select the "Discard Objects" section.
4. Check the "Delete hidden layer contents and flatten visible layers" option.
5. Click OK to finalize the changes.

This can significantly reduce the size of PDF files that contain many layers or that were originally created in graphic design software.

2.6. Removing unused elements

Annotations, embedded thumbnails, and other non-essential elements can make your PDF file larger than its required size. Removing these can help reduce the size:

1. Open your PDF in Adobe Acrobat Pro.
2. Go to File > Save As Other > Optimized PDF.
3. Under the “Discard Objects” tab, select the elements to discard (e.g., comments, form fields, embedded page thumbnails, etc.) that are not essential to your document.
4. Choose the appropriate option and click OK to save your small document.

2.7. Compressing fonts

Fonts, especially custom or highly embedded fonts, can add a lot of weight to a PDF file. Compressing or unembedding fonts can effectively reduce the size.

1. Open your PDF in Adobe Acrobat Pro.
2. Go to File > Save As Other > Optimized PDF.
3. Switch to the "Fonts" tab in the PDF Optimizer window.
4. Check the options to unembed fonts if possible or subgroup fonts to include only the characters that are used within the document.
5. Apply the changes by clicking OK.

Keep in mind that unembedding a font may affect the way the document appears on computers that don't have the same fonts installed.

3. Conclusion

Using the various techniques mentioned above, you can effectively reduce and optimize the file size of your PDF documents using Adobe Acrobat Reader. The choice of methods depends on the specific components and features of your PDF. It is important to balance quality and size, as optimal size reduction should not compromise the essential quality features of your document. As you apply these solutions, constantly preview the converted document to ensure that all essential features are retained and rendered as expected. File optimization is an iterative process, and finding the right balance may require trying several options and adjusting parameters appropriately. However, with informed choices and effective use of Acrobat's extensive tools, you should be able to effectively obtain a well-optimized PDF suitable for sharing and storing.

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