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What is your objective here? What are you trying to do?
Yes, there are a variety of formats that a PDF can be converted to (see below), but each has its own advantages and disadvantages. As far as trying to get any given PDF down to a specific file size, there are obstacles. For example, if the PDF is filled with images, there's only so far you can reduce the final size as images take up a lot of storage space.
BTW, just so you know, Acrobat Pro provides the most capabilities, but Acrobat Reader provides none essentially. Reader provides the ability to read PDFs, fill in forms, make comments, and a few other basic capabilities.
 
I am sorry for the delay, but at a certain point, I do walk away from the computer. I, like most people here, are volunteers and do not work for Adobe.
To answer your question quickly, the answer is no, you cannot tell Acrobat that you want this document to be under 100 kb.
The transition from PDF to any other format is not always clear-cut. One of the values of PDF is it can contain vector and bitmapped information in the same document to obtain the best of both formats. For example, text from a word processor is a vector-type of image. An image from a camera is a bit-mapped format. If I take a full 8.5 x 11 inch document and scan that into a TIF image, it will be about 20 MB. But, if I convert that document into a PDF and then OCR the text, it will be between 80–150kb. Part of the reason for this is that initially, I have 100% of that page is now an image and each pixel, white or black, has to be accounted for. Once it's OCRed, you only have to account for the vector text and vector images are always smaller than a bitmapped image of text.
I just did a quick test. I took a single PDF with just text on one page and saved it as a PDF. It was 58 kb. I then saved the document into a JPG, it was 3.5 MB. Then I saved it into a PNG document and it was 644 kb.
In addition, one of the problems of converting any text from something else to JPG is JPG degredation. By this, I mean that to decrease the size of a JPG, the computer tosses out data that it thinks the image doesn't need. The more compression, the greater the amount tossed and the more degredation there is. This screenshot is the defalt JPG setting in Acrobat.
Look closely around each letter and you'll see stray pixels making it look "dirty." In photographs you'll almost never see this unless you have something like a telephone pole against a sky.
Here's the same text but in PNG format
This is very clean for a variety of reasons, but it still over 100% larger than the original PDF.
If your document has any any bitmapped (like a photograph) images on it, if you save them into a PNG, it will either be significantly larger or lose a lot of its fidelity (and still be larger) depending on whether you save it as a PNG-24 or PNG-8.
So, simply put, you are best to simply run the document through Acrobat's Reduce File Size process and hope for the best. If you have bitmapped image, try and reduce the size of them before placing them in the document (if you reduce an image by 50% in size, it will reduce the storage size of the final image by 400%. And to do this, I mean if your image is 1000 pixels wide, you need to reduce it down to 500 pixels wide. I do NOT mean dragging a corner of the image to decrease the size on the page.). Also, vector images are always smaller than a bitmapped image.
Lastly, there is a lot you can do, but you need to know the mechanics of what you're doing to get the best results.
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