The easiest way how to achieve cdr to ai conversion is to have both programs and export the CorelDraw graphics so you can directly import it to Adobe Illustrator. The crucial question for a successful conversion will be, how the CorelDraw artwork has been originally exported. In case you need to work with layers, go to Tools ► Object manager and create all layer you need and each object will be stored in the layer you have selected. Illustrator will preserve all the layers from CorelDRAW, so when you export your artwork as Illustrator's AI format, select the proper Illustrator version (the one you have installed, instead the default version offered by default in CorelDRAW.
If you do not have access to neither of these program, you will have to rely on 3rd party alternatives.. such as the UniConverter. Just keep in mind that because both AI and CDR formats are proprietary, 3rd party software might not support every version of these format and almost certainly not the latest one.
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