Slow, what are you trying to achieve? Are you just trying to smooth out some low or rough spots, or are you trying to weatherproof?
What is the door made of and what do you plan to do for the final finish?
Bondo is a polyester resin with filler fibers already added. It is not compatible with most of the foam insulation that we use and some things don't like to stick to it. It will absorb moisture if not sealed by additional stages of finish (sealer/primer coat, top coat).
Straight epoxy (resin + hardener) won't add much strength by itself and probably won't keep wood from checking and cracking later; and it doesn't make a good fairing compound all by itself (although you can buy pre-thickened epoxy resins know as epoxy fairing compounds). It does make a pretty good sealer, but is generally not UV resistant, so needs to be prepared and painted or covered in varnish after curing. The first prep stage after curing is to wash it off with water using a green scrubby pad and paper towels. The chemical reaction causes a waxy substance called amine to "bloom" to the surface, and you don't want to spread this around with your sandpaper, etc., or the next thing you do might fail to stick.
If you add fillers (chopped glass fibers, micro balloons, cabosil, etc... available separately) to epoxy it can act a lot like (even just like) Bondo, but won't eat the foam. Depending on the filler used, it may or may not absorb moisture, but most systems call for a couple of "barrier coats" of "neat" (unthickened) epoxy as a sealer coat to seal up any porosity from sanding into the fillers.
If you are wanting to add strength and puncture resistance to the door panel, then glass cloth, or weave, should be used. As I understand it glass mat (with chunky random laid fibers) should only be used with polyester or vinylester resins because the binders used to hold the mat fibers together (and in some types of glass cloth) are not compatible with epoxy; so always tell your sales person which system you are using at the time of purchase, just to be sure.
Unlike Bondo, epoxies have to be mixed at fairly exact ratios, so if you plan to do very much of it there is the added expense of the metering pumps and/or a digital scale (I use both for every batch as a double check).
And here is the big thing, Personal Protective Equipment (PPE). If you plan to handle, use, cleanup and/or sand any of these chemicals you
must know how to properly use a carbon filter style cartridge respirator (not just a dust mask), wear disposable rubber gloves and sleeves, and wear at least safety glasses with side shields.
Soooo, to answer your question, no, you can not glass a door if you don't use any glass.
To be honest, doing fiberglass properly can be quite complicated. I've been working with it for a while now and am still not sure that I am using the optimum methods.
Let's recap some terminology as I understand it:
Bondo - brand name 2 part thermo-setting Polyester fairing compound.
Epoxy - 2 part thermo-setting plastic adhesive containing epoxides.
Resin - can refer to the resin part of a 2 part system, but is sometimes used to refer to a mixture of resin and hardener; sometimes used specifically to denote polyester resin as opposed to epoxy.
Neat epoxy - epoxy resin mixed with hardener and nothing else added; sometimes also just referred to as epoxy,
Epoxy/glass - glass cloth laminated with epoxy. Sometimes referred to as a layup. The process of doing a layup may also include the term "wetting out" the glass.
Thickened epoxy (or just "Thick") - neat epoxy mixed with fillers to provide structural strength for joining and/or so it will hold on to vertical or overhead surfaces; or as a fairing compound (certain fillers can be used to make fairing compounds lighter in weight and easier to sand). Some fillers do some tasks better than others (fairing vs. structural bonding); some do okay at either task.
Composite - anything that is made up of two or more materials that when combined result in something that is more useful or stronger than the sum of the parts. Epoxy isn't that strong in tension and can become brittle by itself. Glass cloth is very strong in tension but is floppy and limp. Together they are much more useful.