PeachPDF
PeachPDF.PdfGenerateConfig
PdfGenerateConfig.PdfVersion Property
The PDF version to target. Defaults to Pdf20 (ISO 32000-2), whose output compresses streams with Brotli unless BrotliCompression is turned off. Set it to Pdf17 for a PDF 1.x file that every reader opens. Requesting a PDF/A or PDF/X level while leaving this property alone picks the version that standard needs: PDF 2.0 for the PDF/A-4 levels and X6, and the PDF 1.4, 1.6 or 1.7 file of the earlier ones. Setting it explicitly to something the requested level cannot use - Pdf17 with PDF/A-4 or PDF/X-6, Pdf20 with any earlier level - throws.
public PeachPDF.PdfVersion PdfVersion { get; set; }