Which of the five files to use
SVG is the cut file: a vector with layers separated by colour, and the format Design Space reads properly. DXF is the fallback for Silhouette Studio Basic, whose SVG import is paywalled. PNG is for print-then-cut or sublimation, not cutting. EPS and AI are for Illustrator and Design Space will reject both.
A PDF in the bundle is usually the licence or an instruction sheet, not artwork. Check it anyway, because that is where the seller states what you are allowed to sell.
Why the upload is rejected
"We couldn't upload this file" has four usual causes, in order of frequency: you picked the ZIP rather than the extracted SVG; you picked the EPS or AI; the SVG contains live text in a font your machine does not have; or it embeds a raster image, a filter or a clip path the parser refuses.
Nothing on your side fixes an EPS. Open the extracted SVG instead, and if the seller only shipped EPS, that is a message to the seller rather than a Design Space problem.
It uploaded, but everything is one colour
Design Space separates layers by fill colour and by nothing else. A seller who exported every piece in the same black fill ships a design that arrives as a single layer no matter how carefully it was grouped in their software. Recolour the pieces you want cut separately, or open the SVG in an editor and give each intended layer its own fill before uploading.
This is also behind "the Etsy file will not attach". Attach does not separate anything, it pins pieces to fixed relative positions so the mat layout leaves them where you put them. If pieces are merging rather than moving, that is the fill colour problem above, not an attach problem.
Sticker sheets are a different flow
A sticker bundle ships PNGs at 300 DPI, sometimes with a matching cut-line SVG. Those go through print-then-cut, not a plain cut: print the PNG with registration marks, then let the machine read the marks and cut the contour. Our print-then-cut guide covers the bleed and registration failures that flow tends to produce.
What the purchase actually licenses
Buying a file buys a licence, and the seller sets its terms. Most permit finished physical products, many cap the number of items, and essentially none permit redistributing or reselling the file itself, including inside a bundle of your own.
If the listing is silent, ask before you list. A shop built on a file whose licence forbade commercial use is a takedown waiting for its first good sales month.