# Edit PPTX Decks > Edit, polish, and audit PowerPoint .pptx decks programmatically — reposition and align shapes, swap or regenerate figures, unify fonts and sizes, insert native OMML equations, and catch the defects that only appear once PowerPoint opens the file. Use whenever the user asks to fix a slide's layout, replace a figure in a deck, align or resize elements, add page numbers, "make this slide look better", audit a deck before a talk, or debug something that "looks fine here but is broken/distorted in PowerPoint". Triggers on phrases like "fix the layout on slide N", "replace this image in the pptx", "align these elements", "the logo is distorted in PowerPoint", "check the deck before I present", "add an equation to this slide". - Skill: `quantumbfs/edit-pptx-decks` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add quantumbfs/edit-pptx-decks` - Raw SKILL.md: https://api.skillmd.com/api/skills/quantumbfs/edit-pptx-decks/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Design & Media - Author: QuantumBFS (https://skillmd.com/u/quantumbfs) - Updated: 2026-09-22 - Page: https://skillmd.com/skills/quantumbfs/edit-pptx-decks --- # Edit PowerPoint decks Editing a `.pptx` well is mostly about a **render-and-verify loop**, because neither `python-pptx` nor your intuition tells you what the slide looks like. The loop is: change one thing → render → look at the pixels → measure → repeat. Everything below is written for that loop. `scripts/pptx_tools.py` bundles the parts that are fiddly to redo by hand. ```bash pip install python-pptx pillow pymupdf lxml fonttools # rendering needs LibreOffice (macOS: /Applications/LibreOffice.app) ``` ## The loop ```bash S=${CLAUDE_SKILL_DIR}/scripts/pptx_tools.py python $S audit deck.pptx # before you touch anything python $S render deck.pptx --pages 2,3 --out /tmp/r --width 1500 # ... edit ... python $S render deck.pptx --pages 2 --out /tmp/r ``` Then **read the PNG**, and measure rather than eyeball: PyMuPDF gives you the real geometry of everything on the page, in centimetres. ```python import fitz d = fitz.open("/tmp/r/_proxy.pdf"); p = d[1] # 0-based S = p.rect.width / 33.87 # px per cm for a 16:9 deck for b in p.get_text("dict")["blocks"]: if b["type"] == 0: x0, y0, x1, y1 = [v / S for v in b["bbox"]] print(f"{x0:.2f}-{x1:.2f} {y0:.2f}-{y1:.2f} " f"{''.join(s['text'] for l in b['lines'] for s in l['spans'])[:30]!r}") for im in p.get_images(full=True): for r in p.get_image_rects(im[0]): print(f"image x {r.x0/S:.2f}-{r.x1/S:.2f} y {r.y0/S:.2f}-{r.y1/S:.2f}") ``` This is how you find the *real* free space on a slide. A picture's frame is usually bigger than its ink — a figure with white margins can start 0.4 cm below the top of its box — so laying out against `shape.top` alone produces gaps that look wrong and collisions that look fine. ## What the preview cannot tell you The renderer is LibreOffice, and it disagrees with PowerPoint in specific ways. Know them, or you will "fix" things that were never broken and ship things that are. **Fonts live in two different worlds.** PowerPoint additionally loads fonts Microsoft ships *inside its own app bundles* — Cambria Math, Microsoft YaHei, Arial (`/Applications/Microsoft*.app/Contents/Resources/DFonts`). LibreOffice sees only system-registered fonts. So a deck that renders with square boxes or Latin fallbacks in your preview may be perfect on the presenter's machine, and a font your audit calls "present" may still be missing for the preview. `render` substitutes using the *system* set and `audit` reports using the *PowerPoint* set; keep that distinction if you roll your own. **LibreOffice ignores OMML run properties entirely.** Font and size on `` have no effect — equations render at LibreOffice's own default, at its own width. You cannot size or position an equation from the preview. Measure it with TeX metrics instead and place it analytically: ```python import matplotlib; matplotlib.use("Agg") import matplotlib.pyplot as plt from matplotlib import rcParams rcParams["mathtext.fontset"] = "cm" fig = plt.figure(); r = fig.canvas.get_renderer() t = fig.text(0, 0, r"$\hat H=-\sum_i\frac{\nabla_i^2}{2}+\dots$", fontsize=100) bb = t.get_window_extent(renderer=r) w_em = bb.width * 72 / fig.dpi / 100 # width in em # Cambria Math runs ~15% wider than Computer Modern print(f"at 18pt: {w_em * 1.15 * 18 / 72 * 2.54:.2f} cm wide") ``` To show the user what they will actually get, composite a matplotlib-rendered equation onto a LibreOffice render of the slide *with the equation removed*. Say plainly that the glyphs are a stand-in and the position is real. **Only some defects survive the trip.** Anything in the "Audit" section below is invisible in a LibreOffice PDF and shows up when PowerPoint opens the file. ## Audit `python $S audit deck.pptx` checks, in order: 1. **Dangling relationships** and stale `[Content_Types].xml` defaults — the usual cause of PowerPoint's "needs to be repaired" dialog. 2. **`` with neither `` nor ``.** LibreOffice silently stretches such a picture to its frame; PowerPoint applies its own default and draws the image at native size, so a 360×360 @100 dpi logo (9.1 cm native) in a 3.3 cm frame comes out mangled. The fix: ```xml ``` Add `` in `` while you are there. 3. **Aspect-ratio distortion** — visible pixels *after* `srcRect` cropping versus the frame. `python-pptx` exposes the crop as `crop_left/right/top/ bottom`; a picture is undistorted when `w(1-cl-cr) / h(1-ct-cb) == width/height`. Fix by widening the crop (keeps the layout) or by resizing the frame (keeps the framing) — ask which. 4. **Duplicate shape ids.** Only a real clash matters: an `mc:Choice` / `mc:Fallback` pair legitimately repeats the same id, and every equation PowerPoint has saved produces one. 5. **TIFF parts.** Legal but poorly supported by PowerPoint on Windows, and usually uncompressed. `python $S tiff2png deck.pptx` re-encodes losslessly, rewires the `.rels` and content types, and typically halves the file. 6. **Fonts** that PowerPoint will substitute — but check the *slot* before worrying. A face used only in `` never touches visible text; one in `` / `` / `` does. Fonts in `notesSlides/` are speaker notes and the audience never sees them. Two more worth a manual look: - **``** — PowerPoint shrinks the text by that factor, LibreOffice often does not, so the preview shows text larger than reality. - **`wrap="none"`** (pervasive in Keynote exports). The text renders on one line at its natural width and simply overflows its box. Harmless until it reaches a neighbour or the slide edge; measure with the fonts PowerPoint will actually use. ## Editing **Prefer `python-pptx` for geometry, raw XML for everything it cannot model.** ```python from pptx import Presentation from pptx.util import Cm, Emu prs = Presentation(path); s = prs.slides[1] # 0-based for i, sh in enumerate(s.shapes): print(i, sh.shape_type, sh.name, f"L{Emu(sh.left).cm:.2f} T{Emu(sh.top).cm:.2f} " f"W{Emu(sh.width).cm:.2f} H{Emu(sh.height).cm:.2f}") s.shapes[2].top = Cm(4.60) prs.save(path) ``` Traps: - **Hidden slides.** `slide._element.get("show") == "0"`. Count and review only the shown ones; a 31-slide file can be a 16-slide talk. - **Shapes inside `mc:AlternateContent` are invisible to `python-pptx`.** Every equation saved by PowerPoint lives there. If a shape you can see in the render is missing from `shapes`, that is why — edit the XML. - **`shape.image.blob` is the *uncropped* source.** What the slide shows is the blob after `srcRect`. Apply the crop yourself before comparing or re-using. - **Group children** have their own coordinate space (`chOff`/`chExt`); scaling a group means scaling graphics and repositioning text separately, or the annotations drift off the thing they annotate. **Replacing a figure**: swap the bytes, do not delete and re-add — that preserves the relationship, z-order, crop, and effects. ```bash python $S swap-image deck.pptx --slide 2 # list the pictures python $S swap-image deck.pptx --slide 2 --index 1 --file new.png ``` Render the replacement to the frame's exact aspect ratio, or pad it to that ratio, so the slide geometry never has to change. **Inserting a native OMML equation.** `python-pptx` cannot; inject XML before ``. Build it from small helpers (`m:nary`, `m:f`, `m:sSub`, `m:sSubSup`, `m:d`, `m:acc`) rather than by hand, put `` — *not* the WordprocessingML `` a LaTeX-to-OOXML converter emits — inside every ``, and declare the `a14` namespace on the element itself: ```xml H ``` Validate with `lxml.etree.fromstring` on the whole slide part before saving. When PowerPoint next saves the file it rewrites this into `mc:AlternateContent` with a raster fallback — expect the file to grow, and do not delete the fallback. **Slide-number fields.** A `` carries a literal `` fallback. PowerPoint computes the number from the field and ignores the literal — but **LibreOffice does not evaluate the field at all**, it prints the literal, so without it every headless render and every exported PDF shows a blank page number. Both `python-pptx` saves and hand-rolled XML rewrites strip it. `python $S fix-nums deck.pptx` puts it back — run it **last, after every write**, and again after reordering slides, since the literal then goes stale. This one bites twice: because the numbers are fine in PowerPoint, a page-number regression is invisible to the user and only shows up in your own preview, where it is easy to dismiss as a rendering artifact. It is not. ## Working alongside the user They will have the deck open. Two habits save a lot of lost work: - **Check `mtime` and file size before and after each of your writes.** If the file changed underneath you, PowerPoint saved over your edits — say so, ask them to close it, and redo. A sudden size jump plus new `mc:AlternateContent` blocks means PowerPoint re-saved and rewrote your equations. - **Back up before every write** (all writing subcommands do, to `.bak_YYYYmmdd_HHMMSS`) and keep the backups. They are the only undo, and they are how you restore an original figure byte-for-byte later: ```python from pptx import Presentation blob = Presentation("deck.pptx.bak_20260828_205337").slides[1].shapes[1].image.blob ``` ## Layout judgement - Fix alignment against the *ink*, not the frames: measure from the rendered PDF, and give elements in a column a shared axis. - Match a replacement figure to its neighbours' visual language — a lone clean object beside a dense reference figure reads as contrast; two dense figures read as clutter. - When a slide feels crowded, moving an element to the slide where it carries the argument beats shrinking everything to fit. - Say what you could not verify. If the preview cannot show a font or an equation faithfully, hand over the numbers you used and ask them to confirm in PowerPoint.