PaintShop Pro is my main editing tool, so I don't use PhotoShop very often, but it does sound as though Jochen and Gordon have worked out the cause of your problem.
Their should also be a facility within your program to export/convert your image file into either a JPG or GIF suitable for web use. In the version I have, PhotoShop 6.0, it is called "
Save For Web."
If your original photo is very large (as most digital camera images are these days), you will probably need to resize it first. I would select
IMAGE from the top navigation bar and then
IMAGE SIZE from the drop-down list. In the new window which appears I would input a new pixel width in the first field (let's say 500, for the sake of this example).
It's up to you to decide how large it needs to be in order for everyone to see the detail, but try to remember that a moderately sized image will make it easier for everyone to view your picture without scrolling across the page, and it will also mean you will not need to use as much compression on the final picture to get it within the 100kb limit.
After re-sizing the picture, the next step would be to compress it to a slightly smaller file size. I would select
FILE (from the top) and then
SAVE FOR WEB. In the next window I choose what type of file I want to create (either JPEG or GIF) and the quality of pic I need - LOW, MEDIUM, HIGH or MAXIMUM. Low will, of course, give you a file smaller in size than High, but the quality will be noticeably different. I can see exactly how large the file will be at each different setting by looking in the bottom left corner of this pop-up window, just below the preview image. (My version also provides an approximate download time for the image on a 28.8 kbps modem - i.e a very slow one!
)
Btw, if you need to keep your original photo in it's uncompressed state, it's probably a good idea to either rename your new image or save it to a different location on your computer (e.g a new folder). Otherwise, you could be at risk of overwriting the original image.
PhotoShop does have its own PDF file format as well as the PSD and PDD ones. Perhaps your program is defaulting to that because it was the last one you used? In any case, a JPG file is the type I would recommend you use if you are wanting to upload photographs to the forum.
Hopefully I haven't made things even more confusing for you. Looking forward to seeing some photos of your creations!