You can control the format of the auto-generated proposal numbers and names, and also the PDF name.
This setting is in Company Settings / Customization / Widget Fields.
Select Proposal Widgets for the Record Type on the left side of the screen. You should see Proposal Name and Proposal # in the Basic Information List.
Click the pencil icon on the far right on the Proposal Name row and the Edit Field modal will display.
The default proposal naming convention for a proposal related to an Account is simply the Account Name. For an opportunity, it's the opportunity name. For the PDF, it's #proposal number proposal name.
All three of these naming conventions are customization. They can be any combination of text and variables. The variables are selected and inserted into the name field by clicking the variables button and selecting a variable that you want included in the name.
For proposal number, the default is simply a number starting at 1000 and incrementing by 1 for every new proposal. You can change this by editing the Default Prefix, Starting Number, Increment, and Default Suffix. The Prefix and Suffix can be any combination of variables and text.
In this example, if the account shipping address state was FL, the proposal number would be
SF-FL12400WH2
and each successive proposal would increase the number by 3.
You can toggle the proposal number on for Creation Visible in the Widget Customization section. This setting will make the proposal number display on the new proposal creation modal, where it will be editable before creating a proposal.
You can also edit the proposal name and number on the proposal overview page by clicking the pencil icon in the upper right corner of the Basic Information widget and then clicking Save when you are done with your edits.
Note: Proposal Name and Proposal number must be unique for every proposal. You can only edit the Proposal Name and Number of a Proposal in DRAFT status.