Daniel,
Are you using ArcPad Data Manager in ArcGIS Desktop to check-out data and create the APM? If not, I would recommend utilizing it. Once the check-out is completed it will provide you with the APM file as well as AXF files or SHP files depending on what you selected. These AXF files contain the features, fields, etc. to be viewed and edited in the field. An APM file without the AXF files is kind of like a MXD without a geodatabase or shapefiles within it.
I hope this helps.