OpenDocMan was designed specifically to prevent files from being edited at the same time. Once a file has been checked out, that file will be unavailable for checkout until the file is checked in again.
In order to have that functionality you would need to download and install the InExp plugin from our plugins page.
Due to all the differences in the way systems handle mime types in files, you may encounter a mime-type that the default installation does not recognize. You can use the Admin->Edit File Types tool to add a new file type to the system. Look at the message you receive from the upload error, there should be a mime-type listed on that pages (ex. application/pdf). You would need to add that as an allowed file type.
View is a permission level that will allow the user to see the file in their file list, but they will be unable to download the file for viewing.
Read is a permission level that will allow the user to see and download the file.
The OpenDocMan User Defined Fields (UDF) feature provides a way of adding custom meta information to your files.
For example, lets say you wanted to categorize each of your files into a color. You would create a new UDF (Select List, Text Field, Radio, Sub-select) which would contain a list of all the colors you want to be able to choose from. Once you create the UDF your new option will appear on the Add File and Edit File forms.
You would set them to have “Read” permissions:
View = they see the file in the list but cannot download
Read = they can download it
Modify = they can check-out/check-in the file
Admin = they can modify the file settings