Unlike with Gerber files, there is not a clearly defined standard for the format of drill files. The program does its best to interpret drill files, but sometimes they simply do not contain enough information to do so automatically.
For best results, you should (if possible) configure the NC Drill generator in your CAD system to use 3.3 METRIC format and to include tool diameters in the drill file. For example, in PADS you should use the configuration shown here.
Drill files should always be checked. For example, some drill files have the hole coordinates in inches while the tool diameters are in millimeters, which will lead to incorrect interpretation. Or perhaps the entire file is in millimeters without specifying so, in which case the file will be interpreted as being in inches and will be too large by a factor of 25.4.
Note: If you are having difficulties with a file that has been generated with metric coordinates, open the file in a text editor and add a line containing M71 immediately after the line with a % character (if it exists) or at the beginning of the file.
The Drill tools pane lists all of the drill files which have been linked. Each drill file has a depth (by default Top to bottom) and a type (by default Plated). Right-click on a file to change its hole depth or the plating of all tools.
If the drill tool diameters are defined within the drill file, then these will be automatically interpreted. If the drill tool diameters are listed in a separate file (or not listed at all), then you will need to enter the tool diameters into the program manually.