Invalid Password Issue

Our company is using the library version 1 of Radaee PDF. Our app supports API versions 21 and above. Of late, some of the documents are getting an 'Open failed: Invalid Password" error when trying to open.
We use the method `m_doc.Open(pdf_path, pdf_pswd)` to open those documents. We have completely removed encyrption from the documents and pass pdf_pwd as 'null' when trying to open those documents based on the documentation. Despite that, we see the same error when trying to open the documents.
private static native long open( String path, String password ); --> this seems like a JNI function and I do not have visibility into that. So I am unable to figure out where it is actually erroring out.
Any idea how to resolve this issue?

dear user, i understand as: you are using very old version of PDF SDK, which support Android API 21.
this version may failed in some password protected PDF file.
you want update to last version PDF SDK, but last version of PDF SDK seems support Android 4.0 and above.
so, i shall tell you: native library is support Android API 21 always.
what you need to do is:
1. replace native libraries to your project.
2. replace java codes for package "com.radaee.pdf" to your project.
3. replace all resources from "raw" in viewLib to your project.
4. restore your license key to Global class.
5. resolve error one by one(shall not so many), for your project.
before you decide to apply all these steps above, you'd better backup your old project first.
if you need opengl layout class to your project, you also need to replace package "com.radaee.view" to your project.
all these codes shall support Android API 21.

Just want to clarify this response,
Do you want us to upgrade to the newer version and follow the steps 1-5 in order to do so?
Also, like I mentioned earlier, we have removed password protection from our documents and open with pdf_pwd as null. So theoretically, we should not run into this issue.

yes, i think you'd better update to last version.
because, i'm not sure what issue on that version.
i remeber that old version was published 7 years ago.
in that version, Document.Open(path, null) and Document.Open(path, "") maybe different.
you may try, but you shouldn't expect too much of this.

if Document.Open(path, "") is still failed in old version.
you can download and test last Android version, before apply these steps, to do some evaluation on last version.
if issue still exists in last version, you can attach your PDF file here.