How can I convert the STEP/ IGES files to the solidworks( or autocad, pro-engineer, ..) ?

here is the procedure for opening STEP/IGES files in solidworks
At first,open the STEP/IGES in solidworks.The STEP/IGES model will open as an imported model in solidworks.while opening the STEP file, the software automatically asks Do you wish to run Import Diagnostics on this part?Click yes and select attempt to heal all and click o.k.After that the software automatically asks Do you want to proceed with feature recognition.click yes.now the model will get opened with features
Import Diagnostics tool used to repair imported models.
You can use the Feature Works Property Manager to set most of the Feature Works recognition options.

You can recognize features automatically or interactively. You can use step-by-step recognition with automatic and interactive feature recognition or a combination of these methods. You can also recognize standard features, or sheet metal features.

Do you want to modified some files from Grabcad Library?

When you make your part just use "save as" and change the file format to IGES or STEP. Any of your CAD programs should be able to open these formats and then you can save them as the native format after you are done working with it.

Thanks.