Many people use Excel to draw their graphs. This causes a minor bottleneck for LaTeX users.
I have played with this problem a bit, tried all sorts of solutions, and now recommend that you copy and paste your graphs in to Powerpoint (which is easier to handle) and then use Powerpoint to save the pdf.
1. Draw the graph in Excel by highlighting the data and using the 'Insert Charts' option.
A graph will pop up on your worksheet which is 12.77 cm wide and 7.69cm high (5-by-3 inches)
If you resize the graph, or move it to a new sheet then you will have to experiment a bit to find out the new size. Move the graph to its own sheet, for example, and it will be 24.17-by-17.56 cm (9-by-7 inches). My version of Excel doesn't have the option to actually force the graph area to a given size.
2. Start a new Powerpoint presentation, set the slide size to 12.77-by-7.69, or whatever you have resized the Excel graph to.
3. Copy and Paste the graph area from Excel to Powerpoint
Change the paste options to 'Paste as Picture' which breaks the link with the Excel sheet. Now you can force the graph to a given size (right-click 'Size and Position' but if you have everything right you won't have to).
4. Save the Powerpoint as a pdf.
The pdf will be exactly the same size as the slide and without extra margins and so will slot in to your LaTeX document smoothly.
This sounds like a terrible faff but after you have done it a few times it becomes routine. Good luck!