Files can be added to Company, Note, Task, Project, Estimate and Job detail pages. There are no limits to the number of files that you upload only a per file size limit of 50Mb.
Here are a couple of tips to help you upload your files successfully.
In the "Add File" dialogue box you will notice that there are two steps. The first step is to select a parent folder and the give the file a name. (If you are a Client Portal user you can also decide whether to share the file with your client by selecting the "client visible" tick box"). The second step is to upload a file.
It is important that you follow this order as uploading a file first will not allow you to add a description and/or mark the file as "client visible" without making an edit.