Thanks for sharing the details.
We cannot reproduce this issue using version 19.10 and the code below:
ConversionConfig conversionConfig = new ConversionConfig();
ConversionHandler conversionHandler = new ConversionHandler(conversionConfig);
ImageSaveOptions saveOptions = new ImageSaveOptions();
saveOptions.setConvertFileType(FileType.Jpeg);
String guid = "D:\\Samples\\manager00.pptx";
ConvertedDocument convertedDocumentPath = conversionHandler.convert(guid, saveOptions);
int totalPage=convertedDocumentPath.getPageCount();
for (int i = 1; i <= convertedDocumentPath.getPageCount(); i++) {
convertedDocumentPath.save("D:\\Samples\\output" + i + "." + convertedDocumentPath.getFileType(), i);
}
See the output images.zip (489.1 KB).
However, we noticed one thing, if the presentation file is corrupted (it was damaged for some reason when I extracted it first time), you will get an exception (class com.groupdocs.conversion.internal.c.a.s.internal.da.j: Unknown file format.). We extracted the file again and performed a successful conversion.