XPS is a document package
An XPS/OpenXPS file contains XML page descriptions and referenced resources in a package. Fonts, images and fixed-page layout are needed to reproduce the document.
A PRN extension is not one format
A printer output file may contain PostScript, PCL or other device languages. Those are not interchangeable with XPS. This converter rejects PRN rather than guessing a language and reporting a false success.
Keep the original
The PDF is a new representation. Preserve the original XPS if you need its digital signatures, package structure or a record of the original print output.
Check a real package before a batch
Start with one XPS or OXPS file that opens in a trusted viewer. Select upload mode, choose the file and leave the range empty for a document of no more than 200 pages. The output is a newly written PDF plus an extracted-text file. Keep both beside the original until you have checked the conversion.
If you only have a PRN file, identify the application and printer driver that created it. Reopening the original document and exporting directly to PDF is often the clearest route. Changing .prn to .xps does not create the XML relationships, page resources or fonts that an XPS parser needs, even if the file chooser accepts the new extension.
A package error can indicate a truncated download, a non-XPS file with an XPS extension, or damaged internal relationships. Download or export the source again before trying repeated conversions. The workbench checks the ordinary ZIP package on upload and requires its content-type description; it does not reconstruct missing resources from guesses.
Use the generated two-page sample when checking whether the local engine loads in your browser. It contains actual XPS XML, vector shapes and an embedded font. A successful sample establishes that the runtime works on that device; it does not establish that an unrelated source file has the same supported features or is intact.