TOPIC:

I had given Read and write permissions for first app installs so it will not be the problem. And app supports android versions 11 1o current version.

Are permissions within the manifest or on demand?
Is the application running on Android prior to 6.x?
May you provide one of your PDF file?

Permissions are in manifest, and handled for marshmallow version also.
App is targeted to Android version 4.4+

Here is the code :-
try {
FileManager.deleteFileWithPath(signatureImagePath);
} catch (Exception e) {
logger.error("Unable to delete signature image");
}
String docPath = getDocumentFilePath(annotatedfileId + DeliverItMacros.EXT_DOC_TYPE_PDF,
DeliverItMacros.RELATIVE_CAPTUREDDOCS_FOLDERPATH);
boolean pdfSaved = pdfReaderView.pdfSaveAs(docPath);

Hi,
first of all make sure that your new docPath exists..
If it doesn't exists create it and then save the pdf.

If you are trying to save it in your external card with devices that run Android 6.0+ you must implement something like that : developer.android.com/training/permissions/requesting.html

If the above tips don't work...can you reproduce the issue with the demo version of the library? If yes please send us your pdf so we can check it..