The Problem (Q-score 12, ranked #120th of 303 in the Excel VBA archive)
The scenario as originally posted in 2008
How do I write an Excel workbook to a MemoryStream without first saving it to the file system?
All options within the Microsoft.Office.Interop.Excel.WorkBook save options take a filename.
Why community consensus is tight on this one
Across 303 Excel VBA entries in the archive, the accepted answer here holds niche answer (below median) status — meaning voters are unusually aligned on the right fix.
The Verified Solution — niche answer (below median) (+6)
Verbal answer — walkthrough without a code block
Note: the verified answer is a prose walkthrough. If you need a runnable sample, check Excel VBA entries ranked in the top 10 of the same archive.
I have done extensive work with the PIA and with storing Excel files in a document repository and streaming it out to the browser, and I have not been able to find a solution to using the PIA without first writing the contents to the file system first.
I think that you are going to have to swallow the bullet and deal with the file system as an intermediary. The good news is that you can just give the file a unique name like a guid or use some other tempfilename method (not sure if one exists in .net) and just delete the contents when you are done.
When to Use It — vintage (14+ years old, pre-2013)
Ranked #120th in its category — specialized fit
This pattern sits in the 98% tail relative to the top answer. Reach for it when your scenario closely matches the question title; otherwise browse the Excel VBA archive for a higher-consensus alternative.
What changed between 2008 and 2026
The answer is 18 years old. The Excel VBA object model has been stable across Office 2013, 2016, 2019, 2021, 365, and 2024/2026 LTSC, so the pattern still compiles. Changes that might affect you: 64-bit API declarations (use PtrSafe), blocked macros in downloaded files (Mark-of-the-Web), and the shift toward Office Scripts for web-first workflows.