@yuanwliu,
I have checked opt.zip. The following fonts have been used in your presentation files. However, I am unable to find any of these fonts in opt.zip that I am assuming is list of fonts on your Amazon Ec2 Linux machine.
Can you please ensure availability of the fonts on your end and also share the JDK you have used.
The Following Fonts have been used in presentation: SynonymandAntonymLessonFreebie.pptx
Font Used: Arial
Font Used: Calibri Light
Font Used: Calibri
The Following Fonts have been used in presentation: ppt_file.ppt
Font Used: Arial
Font Used: Wingdings
Font Used: Calibri
Font Used: Times New Roman
Font Used: Tahoma
Font Used: Calibri Light
I am also assuming that you are using the following sample code as it is on your end. The only change needed is updating the presentation and folder name.
String[] fontDir = new String[] { "/opt/content/fonts/" };
FontsLoader.loadExternalFonts(fontDir);
Presentation presentation=new Presentation("Test.pptx");
String nameFolder="Deck_1";
//String[] result = FontsLoader.getFontFolders();
int slideSize = presentation.getSlides().size();
File dir = new File(nameFolder);
dir.mkdirs();
for (int i = 0; i < slideSize; i++) {
BufferedImage bufferedImage = presentation.getSlides().get_Item(i).getThumbnail(2.0f, 2.0f);
int slideNumber = i + 1;
ImageIO.write(bufferedImage, "png", new File(dir, "Slide" + slideNumber + ".PNG"));
}
