Use `all` for the complete source
The `all` keyword includes pages from first to last and remains clear if the document length changes.
Combine pages and ranges
An expression such as `1-3,7,10-12` includes two inclusive ranges and one single page. Whitespace can be ignored, but reversed ranges should be rejected.
Treat duplicates explicitly
If `1-3,3-5` is entered, a safe merger should not silently include page 3 twice unless duplicate output is an advertised feature.
Validate against each source
A page that exists in one PDF may be out of range in another. Keep one semicolon-separated expression per selected file and review the reported mapping.
Map entries after reordering files
Each semicolon-separated entry belongs to the file at the same visible position. If you move a file up or down, reread the whole mapping before merging; a syntactically valid range can still select the wrong pages when it follows a different source. Use an empty entry between semicolons to mean all pages for that position, such as `;2-4` for all pages from the first file and pages two through four from the second. The result manifest reports selected and available page counts for a final cross-check.
Resolve validation errors instead of guessing
An out-of-range page usually means the visible viewer count and the actual selected file do not match, or the file order changed. A reversed range such as `8-3` is rejected; write the pages in ascending order. Overlapping expressions such as `1-4,4-6` are also rejected because they select page four twice. If deliberate duplication is required, create a separate source PDF containing that page or use a tool that explicitly supports repeated pages. Password-protected or corrupt sources must be opened and repaired outside this merger first.