Where the name comes from. SheetStamp reads one zone, the rectangle you draw around the title block on page 1, on every page of the set. Inside that crop it looks for the labels title blocks commonly print, such as SHEET NUMBER, DRAWING NO, SHEET TITLE and REV, and takes the value beside or below each one. Where a block has no labels, it uses the position the values hold on the other pages, and it ignores text that repeats on most pages, such as the project name, when choosing a title.
The name format. Each page gets the sheet number, a spaced hyphen, and the sheet title: A-101 - FIRST FLOOR PLAN. That text becomes the bookmark in a saved copy and the file name when you split. If a page has no sheet number, the name starts with Page and the page number instead. The revision is read and shown in the table so you can check it, but it is not added to the name.
Characters Windows will not accept. File names cannot contain characters such as a slash, colon or question mark. When a sheet title includes one, the split file name replaces it with a space, while the bookmark keeps the text exactly as typed. Very long titles are shortened so the name stays within 120 characters before the extension.
Two pages with the same number. If the set holds the same sheet twice, both rows are flagged as duplicates and each reason names the other page. You can still export: the later page gets its page number added, such as A-101 - FIRST FLOOR PLAN (page 5).pdf, so neither file overwrites the other.
Why every row is worth a glance. Windows text recognition can misread. It can drop a very short isolated mark, such as a one-letter revision or a two-character sheet number like T1. A missed sheet number is flagged as not found; a missed letter revision leaves the cell empty without a flag. A number misread in the usual spot, such as A-107 where the drawing says A-101, is only flagged if it duplicates another sheet. The table opens on Needs review when anything is flagged; after clearing those rows, switch to All pages and read down the Sheet and Title columns before you save.
Renaming really means writing named copies. SheetStamp never renames or edits the PDF you opened. Save one file per sheet writes new files into a folder you pick, and Save bookmarked copy writes one new file whose suggested name is the original name plus -bookmarked. If you also want the received file renamed, do that in File Explorer.