7 Reasons Why Illustrator PDFs are so Big

PDFs have been around for decades and whether you are involved in the print industry or need to attach files to emails from time to time, chances are good that your life would not be the same without PDFs. Simply put, a PDF (Portable Document Format) is a universally accessible and viewable file format that allows various types of content to be seamlessly integrated into a single document. Things like:

  • Text
  • Images
  • Vector graphics
  • Videos and animations
  • Audio
  • Interactive components
  • Hyperlinks
  • Buttons
  • 3D imagery

With so many capabilities housed within the format, it is not surprising that PDF file sizes can become enormous to the point that they are difficult to send, receive, access, and modify. This is particularly the case with PDFs created through Adobe Illustrator TM. Fortunately, there are ways to rein in runaway file sizes but first, you have to know what to look out for. Here are 7 reasons why Illustrator PDFs are so big.

1. Compression Features have not been Utilized

As the name suggests, compression of an Illustrator PDF takes text, line art, and images, and compresses them in order to reduce file size and make the document easier to send and receive. If an Illustrator PDF has not been compressed, a very large file size can be the result. There are two ways of performing compression on an Illustrator PDF:

  1. Standard compression options include Automatic, in which the Illustrator software determines the right balance of file compression and image quality to create a PDF that has been optimized not just in terms of portability, but also retention of original artwork attributes
  2. Image quality compression allows you to select Minimum, Low, Medium, High, and Maximum Quality options for JPEG compression, and 4-bit or 8-bit quality options for ZIP compression of images

Under the right circumstances, compression can be done so that there is very little loss of fidelity compared to the original file.

2. Downsampling has not been Turned On

Another reason why the file size of an Illustrator PDF can be inflated is that the downsampling feature has not been activated. Downsampling is closely related to compression and reduces a PDF’s size by eliminating pixels from color, grayscale, or monochrome images.

Through a process known as interpolation, downsampling removes pixels in one of three ways:

  1. Average downsampling takes a sample area, evaluates the pixels within that limited area, and then applies the calculated color value to an entire section
  2. Subsampling selects a single pixel at the center of a sample area and then applies that color value to an entire section, resulting in reduced file size but with potentially rough, choppy image quality
  3. Bicubic downsampling utilizes a weighted average to achieve colored pixels that produce images that appear better composed but files with this method of downsampling tend to be larger in size

In conjunction with compression, downsampling can yield a reduced Illustrator PDF file size without sacrificing image quality.

3. Fonts are Embedded in the PDF

With respect to text contained in an Illustrator PDF, certain fonts can comprise a thousand or more characters. If a particular file or document utilizes only a small fraction of an entire font library, then the resulting PDF may be unnecessarily weighed down by characters that are embedded in the file but are not being used.

Fortunately, it is possible when saving a file as a PDF in Illustrator to specify whether or not to embed a font depending on if a certain threshold (i.e., a specified percentage of the entire character set) is met.

4. The PDF File has Illustrator Editing Capabilities Preserved

If left alone, many versions of Illustrator will automatically preserve the entire toolset of editing capabilities when creating a PDF version in order to allow editing at a later time. While this is undoubtedly a useful feature it can also make the PDF exceedingly large because it contains a full suite of native editing tools.

If editing a PDF file is not necessary (or a saved Illustrator working file is all that is needed) then by simply unchecking the appropriate dialog box under save options, a PDF file without editing capabilities built-in can be created and the resulting size will be significantly reduced.

5. Pay Attention to Those PDF Presets in Illustrator

To simplify the process of creating PDF files, Illustrator has built-in presets that optimize the creation of different types of PDF files for various end uses. For instance, being one of the preferred file formats of professional printers everywhere, Illustrator PDFs can be configured for maximum quality and imagery in order to yield the highest print quality. As can be expected, however, these PDFs can be huge.

But what if you need an Illustrator PDF for some other purpose? Fortunately, there are other presets that allow PDFs to be created from Illustrator that are more lightweight and smaller in size. For instance, the “X-1 a:2001” save option converts large Illustrator files into relatively small PDFs.

6. The Wrong Save Settings have been Used

If the purpose of creating an Illustrator PDF does not involve future editing or high-quality printing, then selecting the wrong save setting at the beginning can result in a PDF that is unnecessarily large. For instance, perhaps the only reason for creating an Illustrator PDF in the first place is to share the file with a colleague for some input or obtain a client’s approval.

In such instances, simply selecting the “Smallest File Size” option when saving an Illustrator file as a PDF is all it takes to create a PDF that can be easily sent and accessed. In conjunction with this step, it may be advisable to set the image quality to “High” to maintain an acceptable viewing experience.

7. The Original Illustrator File Needs to be Cleaned Up

In some cases, the reason why an Illustrator PDF is so big is not because of the PDF itself, but the original Illustrator file from which the PDF was produced. Illustrator files can often times carry extra baggage in the form of images, swatches, and other features, that can cause file sizes to balloon. Here are a few common examples:

  • Unused swatches, styles, and symbols are weighing down the Illustrator file
  • There are embedded high-resolution raster files in the original Illustrator file when linked images would suffice
  • Embedded images are larger than need be, or have unnecessary attributes (e.g., background colors) that make no visual contribution to the file
  • Excessive anchor points can number in the thousands and bog down an Illustrator file’s size
  • Similarly, duplication of the same element in an Illustrator document (such as individual stars in a starry sky) can greatly inflate the file size

Thus, by trimming the fat, so to speak, from the source Illustrator file, a PDF saved from that document (especially with additional PDF optimization) can be expected to be significantly smaller in size than a PDF made from a file with no such adjustments made.


The signs that an Illustrator PDF is too big can include impossibly long download times or difficulty opening a file using a mobile device. Fortunately, one does not need to be a professional graphic designer to recognize the cause of an Illustrator PDF’s excessive size and address the issue with a straightforward solution.