Someone was editing some old CorelDraw files which were all vector based. They were adding a background bitmap and then overlaying vector items on top.
When they did this with vector objects that were transparent everything in Corel ceased up and slowed to a crawl particularly with when lots of transparent objects were over layered.
Turning the bitmap layer off brought Corel back to life.
It turned out that the original author had used a Lens effect to perform the transparency on the object.
After some investigations we found information in the Corel documentation that stated when a Lens effect is placed on a vector object and the object is then placed over a bitmap the vector object is converted to a bitmap – this is what was heppening with all the transparent objects and obviously the conversion was slowing everything down.
What the original author should have used was the Transparency tool instead – this is located on one of the toolbar icons as a sub option of the icon that is the Interactive Blend Tool by default (click on the little black arrow in the bottom right and you will see the glass shaped transparency tool).
The transparency tool looks a bit odd the first time you see it – a black square and a white square and a lens rectangle in between. Ignore this and use the toolbar that appears at the top. By default the transparency tool is set to Linear which gives you a gradient effect – change this to uniform and then you can just change the percentage number to the right for the transparency required.
This article explains the Transparency tool in more detail:
To change the existing objects we firstly selected all the objects, then turned off the Lens effect (should be a tab on the Object Manager toolbar usually on the right of the screen), then set the transparency using the correct tool.