How to add dll file into a UWP Project

Question

I'm building a UWP Viewer for the Pdfium library(pdfium.dll). pdfium.dll is a c++ class library. In my Visual Studio Solution, I have two UWP projects. First Project(PdfiumViewer) is a UWP Class Library which imports functions from pdfium.dll and creates user controls. Eg:

[DllImport("pdfium.dll")]
public static extern void FPDF_AddRef();

The second project(PdfiumViewer.Demo) is a UWP Blank App and I referenced the first project here So that I can use its user controls in this project. I included pdfium.dll into the bin folder of my second project. But when I run the program, I get an exception saying "Unable to load pdfium.dll".

There is an existing similar Viewers developed for .Net Windows Forms and WPF apps.

I tried to add pdfium.dll as a reference by right-clicking reference -> "Add reference". In all of these cases(.Net WinForm, .Net WPF, UWP), adding it gave me an error. (ERROR : A reference to ....\pdfium.dll could not be added. please make sure that the file is accessible, and that it is a valid assembly or COM component)

I added the pdfium.dll into .Net WinForm and .Net WPF in a similar way(to the bin folder) and run them. Both types of application viewers worked fine.

My Question: Since UWP apps run in a sandbox, Is there a special location to add this dll(pdfium.dll)?

Note: I tried to add the file in different locations. (inside APPX folder, inside bin\Debug folder, inside bin\Debug\x64, etc)

this might be helpful docs.microsoft.com/en-us/cpp/porting/… — Chanaka Anuradh Caldera
I found out that pdfium.dll is needed to be in APPX/x64 folder. Yet I get an exception saying that "System.DllNotFoundException: Unable to load pdfium.dll or one of its dependencies. The specified module could not be found." — Gayashan Rathnavibushana
Please copy your dll to the project folder and set the type as content. — Nico Zhu - MSFT
I debug the code using breakpoints and found out that LoadLibrary(path) returned IntPtr.Zero. File.Exists(path) returned true. Does anyone familiar with pdfium library? Is it possible to use that DLL in a UWP environment? — Gayashan Rathnavibushana

Gayashan Rathnavibushana Gayashan Rathnavibushana · Accepted Answer · 2020-02-25T05:37:20

When adding the dll to the VS UWP Project, follow the below steps.

First, check the dll using a dependency checker and find out whether the dll is needing additional dependencies.( Such as any other dlls)

Then, (1). Right-click the project -> "Add" -> "Add existing item" -> Select the dll -> Choose "Add as Link" Button from the arrowhead in Add button. (2). After adding the dll, Change the properties as "Content" and "Copy if newer".

How to add dll file into a UWP Project

2 Answers