Pdf/x-1a is a printing standerd that means it is saved using only CMYK and a spot colour not RGB coulors. If you have used a programme to convert from a Word document to a PDf doc. then you are usually asked if the doc is for website, prepress etc. If you choose pre-press or similar then it would be fine. If you are unsure just make sure the document is saved using using CMYK. You do this in the saving options.
I hope that makes sense...