Rosina, thanks for your questions, as this will help me streamline my demo to answer your questions. When I download projects from Creative Fabrica, for simplicity's sake, I download everything in the folder, as I have massive amounts of storage space on my hard drive. I generally don't have much time to sort through all the file types while downloading, so I download them all. If I were short on storage space on my drive, I might take time to go through and delete the file types that I don't need.
PDF files might include written instructions. If not, then the images in the PDF file might be used for hand cutting for those who don't have cutters. If they offer JPG and PNG, I download PNG, if I need to choose, because those generally have transparent backgrounds. These import into our software, and allow for quick and clean tracing to add cutting lines. If PNG is not available, then I can use the JPG.
Anyone using the free version of Silhouette Studio will want to get cutting files in DXF format. If you have an upgraded version of Silhouette Studio that uses SVG files, then you don't need the DXF files. For the most part, SVG files work with cutter software.
The fonts can be used as a regular font for typing in Word or any program that uses fonts. If you want to use special features for fonts in Photoshop, you might want to use OTF versions over TTF. OTF will not work in some software such as Brother Canvas Workspace. I am not sure if they work in Cricut Design Space. So if in doubt, you only need the TTF version of a font. If they only offer OTF, that will work for you.
When I purchase files from any site, I save them to special folders. That way I know where to refer others, should they want to purchase the files. So on my computer Documents folder, I made a new folder that I named Designers. Within that folder, I add another folder for the company. For example, I have a folder for CreativeFabrica, where I download all of the files I get from their site. I try to unzip them as I download them to make it easier to browse their contents. I do keep all of the contents of a folder together. Today, when looking for animal designs at CreativeFabrica, I made a new folder and saved all the Animal files that I liked to this Animal folder within my CreativeFabrica folder. Now when I need an animal, I can find it faster. I still keep sets together, because sometimes I am looking for a cutting file, and other times I am looking for printable designs. Sometimes I need backgrounds to print for use as digital paper.
However, I save the fonts to a different folder that I have named MyFonts. Within that folder, I save fonts either by company or by font type. Since I tend to love script fonts, I save script fonts to this folder. When I unzip the font, I decide if this is a font that I want to use right away. If I do need to use it, I go ahead and install it into my system fonts folder. If using Make The Cut or Sure Cuts a Lot, then I can install temporarily as I need a font, then don't have to install permanently in my system fonts folder. Installing too many fonts there really slow down the system.