Laggy Slow Rendering PDF - Problem & Fix

For work I often view PDF drawings exported or printed from AutoCAD, some have 100's of layers, others are quite simple. Some are Laggy Slow Rendering PDF, where layers of CAD drawing appear very slowly after one another, and as the pdf is regenerated as you zoom or scroll you have to wait all over again. 

I have notice over the last few years that some of the more complex drawings are very slow to render, the display of the PDF layers is laggy, and when zoomed in panning around the document this can be quite annoying. 

PC Specs are old, but heavy duty:

• HP XW8400
• 2 x CPU (2 x xeon 5160) 4 Cores in Total
• 2 x Nvidia NVS 300 1GB 
• Samsung EVO SSD
• 16 GB of RAM

Document for test:

• 2MB PDF exported from CAD drawing with around 50 layers. 

In my attempt to diagnose the problem, I have made the following notes: 

1 - CPU - Not a Problem

Are these laggy PDF, caused by a CPU bottleneck. No they are not. In resource monitor I see around 15% usage over 4 cores (2 CPUs), whilst zooming in and out on the PDF, and panning around using grab function. 

2 - GPU - Not a Problem

Monitoring use of  2x 1GB cards in Nvidia Control Centre I see a maximum of 7% usage on one card. So it is not likely that GPU bottleneck is causing problem. 

3 - Disk Read Write - Not a Problem

Nope, very little activity. Whilst causing PDF to lag, and badly render. 

4 - PDF Software - Not a Problem

I am using a very old version of Foxit PDF in 32 bit. Lets swap that for 64 bit Nitro Reader, and see if that works. No it does not help, actually worse using new software. Also tried with PDF Architect same symptoms. 

5 - Hatching In Drawings < Solution 

I have found over time that problem rests with "hatching" or solid colour fill in drawings. For example if an architect has used green colouring in on a section lawn, then that can cause very slow rendering of PDFs.

If the PDF reader you are using have a layer control panel, look for layers labelled hatch, or fill, or area. And deselect these layers I have found this helps in 90% of cases. 

6 - Convert to Image and then back to PDF

I can use PDF Architect to convert the PDF to an image (PNG / JPEG). I then print that image back to a PDF, taking care to keep the paper size the same as original to preserve scaling. This works very well in deed and is my preferred method. 

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