PDF to image before open PDF

Hi. I have a functional question.

Before opening the file, it is necessary to do a caching thumbnail task. because some big pdf file is too slow to show thumbnail list.

so i use this method.

< method start >
String pdfPath = app().getFilePath(App.FileType.PDF,context.getResources().getString(R.string.appknot_pdf_file_name));
String pdf_path = pdfPath;
String pdf_pswd = "";
Document m_doc = new Document();
m_doc.Open(pdf_path, pdf_pswd);
< method end >

but when i use Open method, it occurs error.

how can i use this method before open PDF?

What error exactly? Are you sure you are passing an accessible path?
For more details about the error codes of the open method, please check: www.radaeepdf.com/documentation/javadocs...ng-java.lang.String-

For the thumbnail caching, we recommend-if possible- to generate PDFs that have pre-loaded thumbnails using appropriate tools like (Adobe InDesign). as in this case the library will use these thumbs directly.

Or you are going to need to save the thumbnails in cache and do not delete them.
For this you can check: PDFGridItem.render , here we save in cache the thumbnail of the PDF's first page, you need to do the same but for all the pages.and without deleting them.