Thanks for reaching out. George is right, we do not have experience with these apps. Could you please check how the image looks in Photo Viewer/ Preview/ Photoshop?
If the image shows transparency there, then it could be related to the import mechanism of these (Irfan or pdfxchange) apps.
If the image doesn't look fine in Photo Viewer/ Preview/ Photoshop, please check and confirm if the issue is related to a specific document? If yes, could you please share the document with us? You can upload it to the Creative Cloud (https://helpx.adobe.com/in/creative-cloud/help/share.html) and share the download link.