There are solutions depending on what sort of program you are using to draw your part.
You can of course import your dxf file into LazyCam and then use the text function in LazyCam to write your text.
I use DeskEngrave a free program from
www.DeskCAM.com to write my text to a DXF file then import that dxf file into a drawing I have created with CADX11 (another free-be, but if you get really serious you will want to upgrade - its cheap!). The file is then saved as a DXF and imported into the G-code producing program you are using. Works with both LazyCam and D2NC.
If the part you want to engrave has already been made you can have DeskEngrave produce a G-code that you may be able to use in Mach3. I have never used that option since the part I am making and the engraving have been designed together. But the code appears to be Mach3 friendly.
CADX can be found at
http://www.graytechsoftware.com/D2NC is an inexpensive program ($79.00) although you can download a complete free trial program. It does take some practice before being easy to work with, but I really like it.
D2 can be found at
http://www.d2nc.com/index.htmlAutoCad does not like the dxf files that DeskEngrave creastes and will not create a usable DXF file
Bob @BobsShop - Is not affiliated with DexkCam, CadX, LazyCam, AutoCad, Mach3 or any other entity!