Document Viewer not working for certain PDF files and prompts to download adobe readerIssue When attempting to view certain pdf files in the document viewer you are prompted to download the acrobat reader rather than being able to view the pdf file CauseThe pdf is a pdf portfolio file. These are a special type of pdf that can contain multiple pdf files See https://helpx.adobe.com/acrobat/using/overview-pdf-portfolios.html as such the document viewer cannot preview it.ResolutionThe document viewer cannot view pdf portfolio files