To change the default app that opens particular files in Chrome (such as PDFs or Office files like .xslx and .doc), go in your Files folder, single click on the file you want to open to highlight it, and click on OPEN button on the top right clue bar (see pic below). You will see a drop down with an option to change what app Chrome will use as default. Select the "Change default..." option and select a new default based on the file type (Open with Citrix should not be default).
Generally, you'd want to make sure that View is set as the default for PDF files and Office Editing for Docs, Sheets & Slides is selected for Excel, Word and PowerPoint slides.