Your JSON profile file should include a list of settings that define exactly what kinds of changes you want to apply to your PDF document.
The PDF Optimizer offers a lot of different methods to optimize of a PDF document. The options you select will depend on how you want to change your output PDF documents.
Suppose you have a PDF document that is 18 MB and you want to make it smaller so that the file will be easier to distribute online. If you expect that your readers will be opening the file in a browser window, and it doesn’t matter if the photographs and diagrams in the document appear with a lower resolution, you could make the document smaller by aggressively compressing the images included in the file.
On the other hand, if you are working with a large PDF document that your customers are likely to want to print, but you want to make it smaller so that it downloads and prints more quickly, you probably want to leave the graphics alone. They will need to appear as sharp as possible. But you don’t need interactive content, like form fields, bookmarks, comments, or digital signatures. You can use PDF Optimizer to remove items from the PDF document that will not appear on paper.
Considering building a PDF document that you intend for people to read on smart phones and other mobile devices. In this case you want to compress the document so that it opens as quickly as possible. So you would reduce the size of the images in this case as well, but given that the screens are a lot smaller than a laptop or desktop monitor, you can reduce the resolution of the images in the PDF document to be less than a PDF document that is intended for opening in a browser window.
All of the settings for compressing a document are optional, and are turned off by default. That means then that a setting is only applied if it is included in the JSON file. Flag settings must be set to “ON.” Settings that are turned off do not need to be defined in the JSON profile file. So if you wanted to you could create a custom JSON file with only a single setting, to compress images. Your JSON file might only hold five or six lines of text.
Only use lowercase characters for the keys and values you add to the JSON file.
The methods you can use to optimize a PDF document are sorted into nine categories:
| Images | When a PDF document is created that includes photographs, diagrams or drawings, the original graphic file, such as a JPEG photograph or a PNG image, become images in that PDF file. You can enter settings in the JSON profile file to compress these color, gray scale, or black & white images. | |
| Fonts | PDF documents can travel with the fonts that they need to access to properly render text. Font files can be embedded within the PDF itself. That way, no matter what machine is used to open a PDF file, the PDF is always guaranteed to look the same, and the viewing tool does not need to look for substitute fonts installed on the local desktop or laptop. But these embedded font files can make the PDF larger, maybe a lot larger, if the document needs to express characters from an Asian font set, like Mandarin or Japanese. You can enter settings in your JSON profile file to remove individual font characters or sets that you don’t need, thus reducing the size of the PDF file. | |
| Transparency | It is possible to stack objects, such as graphics, images, text boxes, and form fields, on top of each other on a PDF document. These objects can be partially or fully transparent, and thus can interact in various ways with objects behind them. If a set of transparencies are stacked in a PDF file, each one contributes to the final result that appears on the page, such as the colors blending together into a final color that appears.
To make a PDF document simpler, you can flatten these transparencies. The flattening process combines the layers of content on a PDF page, or a stack of transparent images or colors, and renders the result as a single image, blended color, or set of text. For example, if a digital signature is flattened, the digital certificate key and related properties are removed from the signature field. The name of the person who signed the document and related information, such as the date and time stamp and the signer’s email address, appear on the page as text, but the signature field is no longer interactive. To flatten the transparencies within a PDF document, there needs to be a "transparency/quality" section in the JSON profile file. |
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| Objects | Besides graphic images and font files, a variety of other objects can be saved within a PDF document.
PDF Optimizer is designed to allow you to remove any of these objects from a PDF document. This serves to make the document smaller and easier to distribute. |
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| User Data | It is possible to edit PDF documents using Adobe Acrobat and other viewing and editing tools. For example, when reviewing the content in a PDF document, a user might want to add a comment. It is also possible to attach external files to a PDF document so that the file is saved as a part of the PDF, or embed a hyperlink to a web page. Finally, a user could add metadata. PDF Optimizer can remove any of this content. It can also remove form fields, such as text boxes, check boxes, and radio buttons. | |
| Cleanup | Use the Cleanup features in PDF Optimizer to set compression values for a PDF document. You can compress the entire PDF document or parts of the content, and you can also remove redundant content or select a compression method to use, as well as other changes designed to make a PDF document open more quickly. | |
| General | These options affect the PDF document as a whole, rather than individual features, like images or fonts or bookmarks. The setting provided under General allows you to force PDF Optimizer to generate a PDF output document even if this document will be larger than the input document it is intended to replace. | |
| Color Conversion | You can turn on this feature to direct PDF Optimizer to convert the colors in a PDF document to a color profile you select before optimizing that document. | |
| PDF/A Conversion | A PDF/A, or PDF Archive document, is a type of PDF file that is designed to be stored so that it can be accessed for many years to come. PDF/A documents must be able to be opened and read using viewing tools available in the future, so they are designed to be self-contained. For example, all of the fonts used in a PDF/A document must be embedded within the PDF document itself for the file to be considered PDF/A compliant. You can turn on this option and prompt PDF Optimizer to save a PDF file as PDF/A compliant after the document is optimized. You can also define the color space used and determine how PDF Optimizer should respond to errors during the conversion process. |