Firstly, ensure that:
The system meets the running requirements for On-Screen TakeOff. Many machines do not have sufficient graphics capabilities. If the specs are acceptable and other users can open the drawing, then this is likely to be due to a configuration issue.
The user's configuration can be located in different places, but where it is should be detailed in the installation instructions. Within this configuration folder will be a DimtronixSettings.xml file, which can be opened in Notepad.
The GraphicsDriverOption may be set to Default. If it is, try changing it to Direct3D. If this does not help, try OpenGL, and if that does not help, try Software.
If that does not work, or if no users can open the drawing, it may be because the application which created the drawing uses a newer standard than the drawing engine which TakeOff uses, or the drawing format has non-standard extensions to it.
In most cases, re-saving the drawing to another format/application version will result in a drawing which does open. For PDF files, you could try Print to PDF, as this strips some of the formatting.
Try resetting the SQL database.
If none of this makes a difference, please continue with a support member for further assistance. And if possible, send the drawing to the support team for investigation.