Adobe Illustrator files compress most successfully as PDF files. As with all compression, the quality of the file will decrease slightly. Before starting, check to find the largest file size that can be used for the application of the final document.
Create a new Adobe Illustrator file or open an existing document. Add any desired text or images.
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Select the "File" menu from the menu bar at the top of the screen. Choose the "Save As" option. Type a file name in the "Save As:" box and select a destination for the file. From the drop-down "Format" menu in the same window, select Adobe PDF.
Choose a format. The easiest way to compress a file is to format it for an earlier version of Adobe. On the next window that appears, select the drop-down menu for "compatibility" in the upper-right corner. Choose "Acrobat 4 or later."
On the left side of the same window that appears select the "Compression" menu if you want more in-depth compression. Review the options listed. If the file is not going to be printed and exists as a multi-color image, review the Color Bitmap Image options. Under Color Bitmap Image, select "Average Downsampling To" for a typical compression. For the best result, but also largest file size, select "Bicubic Downsampling To." According to Adobe Online, "bicubic is the slowest but most precise method, resulting in the smoothest gradations." Subsampling" will result in the poorest quality, but also the smallest file size. Select the drop-down menu and choose "Automatic." In the "Image quality" drop-down menu, select an option between Medium to Maximum, depending on the desired quality.
Select "Save PDF" at the bottom of the window.
Check the file size to see if it is the desired size. If not, open the file in Adobe Acrobat Professional. Select the "Document" menu and choose "Reduce File Size." Select "OK." Check to see if the file is significantly smaller.