Hello hsh,
Welcome to the PhD forum.
.psd & .ai are proprietry formats of Photoshop & Adobe Illustrator, so (without that software) you will not be able to open those files as intended i.e. with editable layers.
You can open .psd files as flattened images in various freeware graphics applications - GIMP, Paint.NET, IrfanView are a few. Saved as .jpg, .png or .tif you can open them in PhD.
.ai files should open in GIMP & (freeware) Inkscape.
PIX
PIX YouTube channel