What dimensions are your Word file? Letter size or 18x24? When you say you converted to PDF, how did you do so?
Did you save as or export the file from Word to make the PDF?
Even if you have the file as 8.5 x11 in Word, you can save as or export as a PDF, (I rarely use Word, but I know there is more than one way to make a PDF from Word)
Staples will be able to print your 8.5x11 PDF at 210%.
The important thing to remember is if there are images in your file they need to have enough resolution so they can be printed without pixelation.
Usually 240 - 300 ppi (pixels per inch)at the final output size are needed to keep it from looking like crap.
If your PDF is being printed at twice the size it will cut the resolution in half!