Do you mean that you unzipped a file and then copied it onto your web server? I have learned from many sad experiences to always rename whatever I'm going to replace, e.g., from flumm.ox to flummBAK.ox.
There are several different ways of signaling the end of lines in raw text files. One is with a carriage return (CR), one is with a line feed (LF), and one is with both, carriage return life feed (CRLF). Looking at my copy of admin.php, it seems to use OA which is the hexadecimal code for a line feed. So if I follow out the logic of the situation (which is all I can do since I don't have the real file as it exists in digital form on your system), it would seem that a file for a plugin was unzipped, and the unzipping software, or perhaps the other guy's zipping software, replaced an OD (carriage return) with an OA (line feed). Anyway, your admin page looks weird because it is not only the wrong content but also has the wrong line terminations.
I've put lots of plugins into my own wiki setup, but I've never had to deal with a zipped file.
However, something worse happened. Your admin page has been replaced by the mangled plugin. How that happened, I can't imagine.
Do you not keep a back copy of your wiki folder on your web server and/or on your HD at home? If you do, you should be able to get an uncontaminated copy of your website to use.
If you do have an unimpaired copy of your wiki files somewhere, copy it to your home HD and lock it so you will always have that to fall back on.
If you do not have an unimpaired copy of your wiki files as they exist on your web served, copy all those external files to a new folder on your home computer and lock it so that at least you will not ever lose what you now have left of your total set of wiki files.
After writing the above I tried to find what your were talking about when your wrote "I installed a zip," After much futile searching for a zip file in the website of Prof. Plsch, I came all the way around and discovered that you must have found an OLD plugin by going through the plugins that are available on DokuWiki and you must have tried to install ZIP PLUGIN. Whatever you did went drastically wrong. Next time, after you have checked with compatibility with the system of DokuWiki you are running ("zip plugin" is not compatible with your DokuWiki, I suspect), then to your Administration page, choose extension manager, search for the name of the plugin you want, and you will be guided from there on.
This is getting too abstract since I'm guessing about what you actually did.
Please confirm any parts of my conjecture that are correct.
Please indicate whether or not you have an old copy of your wiki folder that hasn't been contaminated by the replacement of php files intended for your admin page by the mangled (?) "zip plugin."