Flattening a Complex PDF File
If your PDF file takes a long time to open, and you can see each layer being drawn on your screen one at a time, it is a good indication that you will not be able to print it. Here are a few techniques for making a complex file printable.
Merge Your Layers
If you have multiple layers in your project file you should merge them together by combining them into one layer. Make sure to do this in a copy of your project file because merging layers cannot be undone.
Create a Print-Ready PDF using Adobe Acrobat
Follow Adobe’s guide to saving to the print-optimized PDF X-4 file type
Print to PDF
Print-to-PDF using the Adobe PDF Printer (installed with Adobe Acrobat DC) is the best way to generate a printable PDF file. This is the first step in reducing the complexity of your document. Do not Export or Save to PDF from applications like Illustrator or InDesign.
Sanitize PDF in Adobe Acrobat
Adobe offers a feature previously called Sanitize Document, and now called simply “Remove Hidden Information”
This feature is designed to remove hidden personal information from a document before it is distributed, A nice side-effect of this process is that it creates a much flatter version of a PDF that is easier to print. In Acrobat DC select TOOLS -> PROTECT -> REMOVE HIDDEN INFORMATION. Now try to print your file!
Print as Image
Alternatively, you can save your PDF or InDesign File as a .jpg and print it from Photoshop.
Do Not Compress your File
When you send a compressed file to the printer the printer has to uncompress it. So, you are actually adding to the processing load! A small file is not necessarily a flattened file.