A customer provided art file can be pretty slippery due to odd ways and bad choices of how the artwork may have been created, exported or even round-tripped thru multiple applications before the file was sent to you in its present condition.
Poor quality artwork is not too bad a hassle if all you have to do is print it. Most of the files I receive are intended for permanent signs and require further editing. So they need to be of a higher standard (preferably 100% vector-based).
PDF-based files are a common source for trouble. The only "good" PDF files I see are ones generated by Adobe Illustrator and saved with the option to preserve Illustrator editing capability. Most applications generate PDFs to be web friendly, which means doing all sorts of crazy things to the artwork to reduce file size and ensure backward compatibility with older web browsers and PDF readers. Opening one of these kinds of PDF files in Adobe Illustrator often reveals a horrible mess. You'll find lots of clipping masks, clipping groups, duplicate copies of objects that have no fill or stroke, broken open or sliced paths, rasterized objects and more. A tool like Astute Graphics' Vector First Aid plug-in for Adobe Illustrator can fix/repair many issues in junky PDFs and save a great deal of editing time. But often there will be some manual steps needed to finish repairing the artwork, such as using the eye-dropper tool to re-apply gradients to objects from gradient filled boxes that were previously clipped to that parent object.
EPS files can also be a big problem depending on what features and effects were used in the host graphics application before the EPS file was exported. Depending on the version of EPS chosen in the dialog box, along with other options, various features in the artwork may "break" or be simulated, such as a gradient fill being turned into hundreds of sliced objects.
I move a lot of artwork between Adobe Illustrator and CorelDRAW frequently and don't really see that problem with gradient filled objects. Usually the gradient fill is maintained as a vector object. However, the size/position of the gradient and its steps may shift a little or a lot. I usually get the best results by using the latest AI file format both applications can read.
Gradient fill behavior has changed a lot since 1997. Illustrator has supported non-symmetrical gradients and steps of transparency on gradients for a long time. CorelDRAW matched those features in CDR X8 and CDR 2018. Now Illustrator has the free-form gradient feature that opens a whole new can of worms. Thank goodness Onyx and RasterLink Pro support it in EPS and PDFs exported from Illustrator.
